Method for in vitro proliferation of dendritic cell precursors and their use to produce immunogens

ABSTRACT

A method for producing proliferating cultures of dendritic cell precursors is provided. Also provided is a method for producing mature dendritic cells in culture from the proliferating dendritic cell precursors. The cultures of mature dendritic cells provide an effective means of producing novel T cell dependent antigens comprised of dendritic cell modified antigens or dendritic cells pulsed with antigen, including particulates, which antigen is processed and expressed on the antigen-activated dendritic cell. The novel antigens of the invention may be used as immunogens for vaccines or for the treatment of disease. These antigens may also be used to treat autoimmune diseases such as juvenile diabetes and multiple sclerosis.

This application is continuation-in-part of U.S. patent application Ser.No. 08/040,677 filed Mar. 31, 1993, which is a continuation-in-part ofU.S. patent application Ser. No. 07/981,357 filed Nov. 25, 1992 which inturn is a continuation-in-part of U.S. patent application Ser. No.07/861,612 filed Apr. 1, 1992.

This invention was made with United States Government support under NIHgrant AI13013 awarded by the National Institutes of Health. The UnitedStates Government has certain rights in this invention. The making ofthis invention was also supported by the Austrian Government throughgrants NB 4370 (Austrian National Bank) and P 8549M (Austrian ScienceFoundation); and by Austrian National Bank (JUBILAEUMSFONDS PROJECT4889).

TECHNICAL FIELD OF THE INVENTION

This invention relates to a method of culturing cells of the immunesystem. In particular a method is provided for culturing proliferatingdendritic cell precursors and for their maturation in vitro to maturedendritic cells. This invention also relates to dendritic cell modifiedantigens which are T cell dependent, the method of making them, andtheir use as immunogens. Vaccines, methods of immunizing animals andhumans using the mature dendritic cells of the invention, and themodified antigens are also described.

BACKGROUND OF THE INVENTION

The immune system contains a system of dendritic cells that isspecialized to present antigens and initiate several T-dependent immuneresponses. Dendritic cells are distributed widely throughout the body invarious tissues. The distribution of dendritic cells has been reviewedin (1). Dendritic cells are found in nonlymphoid organs either close tobody surfaces, as in the skin and airways, or in interstitial regions oforgans like heart and liver. Dendritic cells, possibly under the controlof the cytokine granulocyte macrophage colony-stimulating factor,(hereinafter GM-CSF), can undergo a maturation process that does notentail cell proliferation (2, 3). Initially, the dendritic cells processand present antigens most likely on abundant, newly synthesized MHCclass II molecules, and then strong accessory and cell-cell adhesionfunctions are acquired (4-7). Dendritic cells can migrate via the bloodand lymph to lymphoid organs (8-10). There, presumably as the“interdigitating” cells of the T-area (8, 11-13), antigens can bepresented to T cells in the recirculating pool (14). However, little isknown about the progenitors of dendritic cells in the differentcompartments outlined above.

The efficacy of dendritic cells in delivering antigens in such a waythat a strong immune response ensues i.e., “immunogenicity”, is widelyacknowledged, but the use of these cells is hampered by the fact thatthere are very few in any given organ. In human blood, for example,about 0.1% of the white cells are dendritic cells (25) and these havenot been induced to grow until this time. Similarly, previous studies(20, 21) have not reported the development, in culture, of large numbersof dendritic cells from bone marrow. A more recent report described thedevelopment of dendritic cells in GM-CSF supplemented marrow cultures,however no documentation as to the origin of the dendritic cells or useof proliferating aggregates as an enriched source of dendritic cells wasobserved. (Scheicher et al. (1992)) J. Immunol. Method. 154:253-264.While dendritic cells can process foreign antigens into peptides thatimmunologically active T cells must recognize (4, 6, 7, 14) i.e.,dendritic cells accomplish the phenomenon of “antigen presentation”, thelow numbers of dendritic cells prohibits their use in identifyingimmunogenic peptides.

Dendritic cells in spleen (15) and afferent lymph (16, 17) are not inthe cell cycle but arise from a proliferating precursor. Ultimately,dendritic cells emanate from the bone marrow (15, 16, 18, 19), yet ithas been difficult to generate these cells in culture except for tworeports describing their formation in small numbers (20, 21). Although abone marrow precursor cell has been reported, conditions have not beenreported that direct its proliferation in culture (Steinman, R. (1991))“The Dendritic Cell System and Its Role In Immunogenicity”, Ann. Rev.Immunol., 9:271-96. Identification of proliferating dendritic cells inbone marrow, in contrast to blood, is difficult because there are largenumbers of granulocytes that develop in response to GM-CSF and thesecrowd the immature dendritic cell cultures, preventing maturation of thedendritic precursors. The use of cell surface markers to enrich bonemarrow dendritic cell precursors has been reported to result in onlymodest increases because the markers are also expressed by numerousnon-dendritic bone marrow cells (Bowers, W. E. and Goodell (1989)),“Dendritic Cell Ontogeny” Res. Immunol. 140:880-883.

Relatively small numbers of dendritic cells have also been isolated fromblood (Vakkila J. et al. (1990) “Human Peripheral blood-deriveddendritic cells do not produce interleukin 1α, interleukin 1β, orinterleukin 6” Scand. J. Immunol. 31:345-352; Van Voorhis W. C. et al.,(1982) “Human Dendritic Cells”, J. Exp. Med., 1172-1187.) However, thepresence in blood of dendritic cell precursors has not been reported andas recently as 1989 the relationship between blood dendritic cells andmature dendritic cells in other tissues was uncertain. Furthermore, itwas recognized that dendritic cells are “rare and difficult to isolateand have not as yet been shown to give rise to DC [dendritic cells] inperipheral tissues.” (MacPherson G. G. (1989) “Lymphoid Dendritic cells:Their life history and roles in immune responses”, Res. Immunol.140:877-926).

Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a factorwhich modulates the maturation and function of dendritic cells.(Witmer-Pack et al, (1987) “Granulocyte/macrophage colony-stimulatingfactor is essential for the viability and function of cultured murineepidermal Langerhans cells”. J. Exp. Med. 166:1484-1498; Heufler C. etal., (1988) “Granulocyte/macrophage colony-stimulating factor andinterleukin 1 mediate the maturation of murine epidermal Langerhanscells into potent immunostimulatory dendritic cells”, J. Exp. Med.167:700-705). GM-CSF stimulated maturation of dendritic cells in vitrosuggests that the presence of GM-CSF in a culture of dendritic cellprecursors would mediate maturation into immunologically active cells,but the important goal of achieving extensive dendritic cell growth hasyet to be solved.

T-dependent immune responses are characterized by the activation ofT-helper cells in the production of antibody by B cells. An advantage ofT-dependent over T-independent immune responses is that the T-dependentresponses have memory, i.e. cells remain primed to respond to antigenwith rapid production of antibody even in the absence of antigen and theimmune response is therefore “boostable”. T-independent immune responsesare, in contrast, relatively poor in children and lack a boosterresponse when a T-independent antigen is repeatedly administered. Theimmunologic memory of T cells likely reflects two consequences of thefirst, “primary” or “sensitizing” limb of the immune response: (a) anexpanded number of antigen-specific T cells that grow in response toantigen-bearing dendritic cells, and (b) the enhanced functionalproperties of individual T cells that occurs after dendritic cellpriming (Inaba et al., (1984) Resting and sensitized T lymphocytesexhibit distinct stimulatory (antigen presenting cell) requirements forgrowth and lymphokine release; J. Exp. Med. 160:868-876; Inaba andSteinman, (1985) “Protein-specific helper T lymphocyte formationinitiated by dendritic cells”, Science 229: 475-479; Inaba et al.,(1985) “Properties of memory T lymphocytes isolated from the mixedleukocyte reaction”, Proc. Natl. Acad. Sci. 82:7686-7690).

Certain types of antigens characteristically elicit T-cell dependentantibody responses whereas others elicit a T-cell independent response.For example, polysaccharides generally elicit a T-cell independentimmune response. There is no memory response and therefore no protectionto subsequent infection with the polysaccharide antigen. Proteins,however, do elicit a T-cell dependent response in infants. Thedevelopment of conjugate vaccines containing a polysaccharide covalentlycoupled to a protein converts the polysaccharide T-independent responseto a T-dependent response. Unfortunately, little is known concerning thesites on proteins which confer their T-cell dependent character,therefore hampering the design of more specific immunogens.

As stated above, dendritic cells play a crucial role in the initiationof T-cell dependent responses. Dendritic cells bind and modify antigensin a manner such that the modified antigen when presented on the surfaceof the dendritic cell can activate T-cells to participate in theeventual production of antibodies. The modification of antigens bydendritic cells may, for example, include fragmenting a protein toproduce peptides which have regions which specifically are capable ofactivating T-cells.

The events whereby cells fragment antigens into peptides, and thenpresent these peptides in association with products of the majorhistocompatibility complex, (MHC) are termed “antigen presentation”. TheMHC is a region of highly polymorphic genes whose products are expressedon the surfaces of a variety of cells. MHC antigens are the principaldeterminants of graft rejection. Two different types of MHC geneproducts, class I and class II MHC molecules, have been identified. Tcells recognize foreign antigens bound to only one specific class I orclass II MHC molecule. The patterns of antigen association with class Ior class II MHC molecules determine which T cells are stimulated. Forinstance, peptide fragments derived from extra cellular proteins usuallybind to class II MHC molecules, whereas proteins endogenouslytranscribed in dendritic cells generally associate with newlysynthesized class I MHC molecules. As a consequence, exogenously andendogenously synthesized proteins are typically recognized by distinct Tcell populations.

Dendritic cells are specialized antigen presenting-cells in the immuneresponse of whole animals (14, 31). Again however, the ability to usedendritic cells to identify and extract the immunogenic peptides ishampered by the small numbers of these specialized antigen presentingcells.

Particle uptake is a specialized activity of mononuclear andpolymorphonuclear phagocytes. Dead cells, immune complexes, andmicroorganisms all are avidly internalized. Following fusion withhydrolase-rich lysosomes, the ingested particles are degraded (60, 61).This degradation must be to the level of permeable amino acids (62, 63)and saccharides, otherwise the vacuolar apparatus would swell withindigestible materials (64, 65). Such clearance and digestive functionsof phagocytes contribute to wound healing, tissue remodeling, and hostdefense.

Another consequence of endocytosis, the processing of antigens byantigen presenting cells (APCs), differs in many respects from thescavenging function of phagpcytosis. First, processing requires thegeneration of peptides at least 8-18 amino acids in length (66, 67),while scavenging entails digestion to amino acids (62, 63). Secondly,presentation requires the binding of peptides to MHC class II products(6, 68), whereas scavenging does not require MHC products. Thirdly,antigen presentation can function at a low capacity, since only a fewhundred molecules of ligand need to be generated for successfulstimulation of certain T-T hybrids (69, 70) and primary T cellpopulations (71). During scavenging, phagocytes readily clear anddestroy hundreds of thousands of protein molecules each hour (63).Lastly, antigen presentation is best carried out by cells that are richin MHC class II but show little phagocytic activity and few lysosomes,i.e., dendritic cells and B cells, while phagocytes (macrophages andneutrophils) often have low levels of class II and abundant lysosomes.These observations, together with the identification of antigenicspecializations within the endocytic system of dendritic cells and Bcells, have lead to the suggestion that the machinery required forantigen presentation may differ from that required for scavenging, bothquantitatively and qualitatively (31).

In the case of dendritic cells, there have been indications that theseAPCs are at some point during their lifetime capable of phagocyticactivity. Pugh et al. noted Feulgen-stained inclusions in some afferentlymph dendritic cells and suggested that phagocytosis of other cells hadtaken place prior to entry into the lymph (16). Fossum noted phagocyticinclusions in the interdigitating dendritic cells of the T cell areas inmice that were rejecting allogeneic leukocytes (71). Reis e Sousa et al.(74) found that freshly isolated epidermal Langerhans cells, which areimmature but nonproliferating dendritic cells, internalize small amountsof certain particulates. Neither report, however, demonstrates orsuggests the occurrence of phagocytosis when particles are administeredto cultures of proliferating dendritic cells.

Injection of dendritic cells pulsed with pathogenic lymphocytes intomammals to elicit an active immune response against lymphoma is thesubject of PCT patent application WO 91/13632. In addition, Francotteand Urbain, Proc. Nat'l. Acad. Sci. USA 82:8149 (1985) reported thatmouse dendritic cells, pulsed in vitro with virus and injected back intomice, enhances the primary response and the secondary response to thevirus. Neither the report by Francotte and Urbain and patent applicationWO 91/13632 provide a practical method of using dendritic cells as anadjuvant to activate the immune response because both of these methodsdepend on dendritic cells obtained from spleen, an impractical source ofcells for most therapies or immunization procedures. In addition,neither report provides a method to obtain dendritic cells in sufficientquantities to be clinically useful.

SUMMARY OF THE INVENTION

This invention provides a method of producing a population of dendriticcell precursors from proliferating cell cultures. The method comprises(a) providing a tissue source comprising dendritic cell precursors; (b)treating the tissue source from (a) to increase the proportion ofdendritic cell precursors to obtain a population of cells suitable forculture in vitro; (c) culturing the tissue source on a substrate in aculture medium comprising GM-CSF, or a biologically active derivative ofGM-CSF, to obtain proliferating nonadherent cells and cell clusters; (d)subculturing the nonadherent cells and cell clusters to produce cellaggregates comprising proliferating dendritic cell precursors; and (e)serially subculturing the cell aggregates one or more times to enrichthe proportion of dendritic cell precursors.

In another embodiment of this invention, cells may be cultured in thepresence of factors which increases the proportion of dendritic cellprecursors by inhibiting the proliferation or maturation ofnon-dendritic cell precursors.

For example, cells may be cultured in the presence of factors whichinhibit macrophage proliferation and/or maturation. Such a factor shouldbe provided in an amount sufficient to promote the proliferation ofdendritic cells while inhibiting the proliferation and/or maturation ofmacrophage precursor cells or macrophages. Examples of such agentsinclude Interleukin-4 (IL-4) and Interleukin-13 (IL-13). These agentsare particularly useful for culturing cells from preferred tissuesources such as blood, and more preferably specifically human bloodisolated from healthy individuals.

This invention also provides a method of producing in vitro maturedendritic cells from proliferating cell cultures. The method comprises(a) providing a tissue source comprising dendritic cell precursor cells;(b) treating the tissue source from (a) to increase the proportion ofdendritic cell precursors in order to obtain a population of cellssuitable for culture in vitro; (c) culturing the tissue source on asubstrate in a culture medium comprising GM-CSF, or a biologicallyactive derivative of GM-CSF, to obtain non-adherent cells and cellclusters; (d) subculturing the nonadherent cells and cell clusters toproduce cell aggregates comprising proliferating dendritic cellprecursors; (e) serially subculturing the cell aggregates one or moretimes to enrich the proportion of dendritic cell precursors; and (f)continuing to culture the dendritic cell precursors for a period of timesufficient to allow them to mature into mature dendritic cells.

To reduce the proportion of non-dendritic precursor cells, the tissuesource may be pretreated prior to culturing the tissue source on asubstrate to obtain the non-adherent cells or during the early stages ofthe culture. Preferred tissue sources for the practice of the inventionare bone marrow and, in particular, blood.

This invention also provides a method of increasing the proportion ofdendritic cells present in the tissue source by pretreating theindividual with a substance to stimulate hematopoiesis.

When bone marrow is used as the tissue source the pretreatment stepcomprises killing cells expressing antigens which are not expressed ondendritic precursor cells by contacting the bone marrow with antibodiesspecific for antigens not present on dendritic precursor cells in amedium comprising complement. Removal of undesirable non-dendritic cellprecursors may also be accomplished by adsorbing the undesirablenon-dendritic or their precursor cells onto a solid support.

This invention also provides dendritic cell precursors and dendriticcells in amounts which may be used therapeutically and which also may beused to prepare new therapeutic antigens. In addition, the dendriticcell precursors and dendritic cells prepared according to the method ofthis invention are also provided.

Another embodiment of the invention are antigen-activated dendriticcells prepared according to the method of the invention in whichantigen-activated dendritic cells have been exposed to antigen andexpress modified antigens for presentation to and activation of T cells.

This invention also provides novel antigens which are produced byexposing an antigen to cultures of dendritic cells prepared according tothe method of the invention in which the antigen is modified by thedendritic cells to produce modified antigens which are immunogenicfragments of the unmodified or native antigen and which fragmentsactivate T cells.

These novel antigens may be used to immunize animals and humans toprevent or treat disease.

This invention also provides a method of preparing antigens fromdendritic cell precursors comprising providing precursor dendritic cellsfrom a population of precursor cells capable of proliferating,contacting the precursor cells with antigen for a period of timesufficient to allow the dendritic cell precursors to phagocytose theantigen and obtain antigen-containing dendritic cell precursors;culturing the antigen containing-dendritic cell precursors underconditions and for a period of time sufficient for the antigen to beprocessed and presented by dendritic cell precursors.

The antigens processed by the dendritic cell precursors as a result ofphagocytosis may themselves be used alone or in combination withadjuvants including dendritic cell precursors to evoke an immuneresponse in an individual to the antigen.

Also provided are compositions and methods for increasing the number ofmyeloic dendritic progenitor cells in blood in those individuals.

In a further embodiment, the yield of dendritic cell precursors isincreased by culturing the precursors in a sufficient amount of GM-CSFand other cytokines to promote proliferation of the dendritic cellprecursors. Other cytokines include but are not limited to G-CSF, M-CSF,TNF-α, Interleukin-3, and Interleukin-1α, Interleukin-1β, Interleukin 6,Interleukin-4, Interleukin-13 and stem cell factor.

In another embodiment, the invention provides self-peptide antigensproduced by pulsing the dendritic cells of the invention with a proteinto which an individual has developed an immune response and extractingthe relevant self-peptide or autoantigen.

This invention also provides a method of treating autoimmune diseases bytreating an individual with therapeutically effective amounts ofself-peptides produced according to the method of the invention toinduce tolerance to the self-proteins.

The treatment of autoimmune diseases comprising administering to anindividual in need of treatment a therapeutically effective amount ofantigen-activated dendritic cells where the antigen is a self-protein orautoantigen is also provided.

The use of the compositions and methods of the invention to treatautoimmune diseases selected from the group of juvenile diabetes,myasthenia gravis, and multiple sclerosis is also provided.

This invention also provides treatment for inflammatory diseases inwhich the pathogenesis involves exaggerated T cell mediated immuneresponses such as those present in atopic dermatitis and contactdermatitis.

This invention also provides a method for providing an antigen to a hostcomprising exposing an antigen to a culture of dendritic cells preparedaccording to the method of this invention to produce antigen-activateddendritic cells followed by inoculating the host with theantigen-activated dendritic cells.

This invention further provides a method of activating T cellscomprising the use of proliferating dendritic cells for capturingprotein, viral, and microbial antigens in an immunogenic form in situand then presenting these antigens in a potent manner to T cells eitherin vitro or in situ.

This invention additionally provides a method comprising the use ofmature and precursor dendritic cells to present MHC class I and IIproducts with antigen peptides.

This invention also provides a method for making antigenic peptides thatare specific for an individual's MHC products thereby increasing thenumber of specialized stimulatory antigenic presenting cells availableto provide an immunogenic response in an individual.

Also provided are compositions and methods to treat infectious diseases,including but not limited to diseases caused by mycobacteria includingtuberculosis, bacteria, and viruses.

Compositions and methods for using dendritic cells or dendritic cellprecursors as vehicles for active immunization and immunotherapy in situare also provided.

Vaccines comprised of any of the antigens or antigen-activated dendriticcells described above are also provided as are the methods of immunizingagainst disease in humans or animals comprising administering any of thecompositions of the invention.

An object of this invention is to provide a method of culturingdendritic cell precursors in vitro so that they evolve into maturedendritic cells suitable for use as immunogens or adjuvants whencombined with an antigen.

It is also an object of this invention to provide dendritic cellprecursors capable of phagocytosing antigenic material to be processedand presented by the dendritic cell precursors.

Another object of this invention is to provide a convenient andpractical source of sufficient quantities of dendritic cells anddendritic cell precursors to be useful in the treatment or prevention ofdisease.

Another object of this invention is to provide novel immunogenscomprising the dendritic cells or dendritic cell precursors of thisinvention which have been exposed to antigen and express modifiedantigen on their surface.

Another object of this invention is to provide antigens which have beenmodified through their exposure to dendritic cell precursors ordendritic cells and which modified antigens are effective as T-celldependent antigens.

A further objective of the invention is to provide a method ofimmunizing individuals with T-cell dependent antigens for the preventionand treatment of disease.

FIGURE LEGENDS

FIG. 1. Flow plan for inducing dendritic cell “colonies.”

FIG. 2. FIG. 2 comprises FIGS. 2A through 2F which are FACS analyses ofdendritic cells released from proliferating aggregates. Several mAbswhich recognize various cell surface determinants on dendritic cellprecursors (23, 24, 28) are shown. Except for MHC class I and IIproducts, the phenotype of the released cells is homogeneous. Thestaining with no primary mAb was identical to RB6 and RA3.

FIG. 3. FIG. 3 comprises FIGS. 3A through 3F which are FACS analyses ofdendritic cell precursors that could be dislodged by Pasteur pipettingof proliferating aggregates, (3A, 3B and 3C) and dendritic cellsreleased spontaneously (3D, 3E and 3F) in culture. The mAb are: M1/42anti-MHC class I [ATCC #TIB 126]; NLDC145 anti-interdigitating cell(13); M5/114 anti-MHC class II [ATCC #TIB 120]; 33D1 anti-dendritic cell[ATCC #TIB 227]; B5-5 anti-thy-1. The staining with anti-MHC mAbs isbimodal, but the released cell fraction of dendritic cells is richest inexpression of MHC class I and II.

FIG. 4. MLR stimulating activity of populations isolated from the GM-CSFstimulated mouse blood cultures [see text].

FIG. 5. (FIGS. 5A-5B) Progressive development of MLR stimulatingactivity in bone marrow cultured in the presence of GM-CSF.

Ia-negative precursors, B and T cell-depleted marrow cells were culturedin GM-CSF with ¾ of the medium being replaced every 2d. At each timepoint, the cells were dislodged by gently pipetting. After irradiation,graded doses of marrow cells were applied to 3×10⁵ allogeneic [C57BL/6,(5A, left)] or syngeneic [BALB/C×DBA/2 F1 (5B)] T cells and cultured for4 days in the MLR. 3H-TdR uptake was measured at 80-94 h [values aremeans of triplicates with standard error bars].

FIG. 6. (FIGS. 6A-6B) Physical properties of the MLR stimulating cellsthat develop in GM-CSF supplemented bone marrow cultures [see text].

6A. Cultures similar to those in FIG. 5 were separated into nonadherent[open symbols] and loosely adherent fractions [closed symbols], thelatter being cells that could be dislodged by gently pipetting over themonolayer. For the d4 separations, loosely adherent cells [mainlygranulocytes] were rinsed away at d2, and for the d6 separation,granulocytes were rinsed away at d2 and d4. The cells were irradiatedand applied in graded doses to allogeneic T cells as in FIG. 5.

6B. At the indicated time points, free cells and cell aggregates weredislodged from the stromal monolayer and separated by 1 g sedimentation.The aggregates were cultured for 1 day to provide released cells. Thesecells were irradiated and tested as MLR stimulators, as were firmlyadherent cells that were dislodged in the presence of 10 mM EDTA [opensquares].

FIG. 7. (FIGS. 7A-7F) Cell cytofluorometry of the development ofIa-positive cells from aggregates within bone marrow culturessupplemented with GM-CSF.

GM-CSF stimulated, bone marrow cultures [left (7A, 7D), unfractionated]were compared with loosely attached cell aggregates [middle (7B, 7E)]and cells released from the aggregates after overnight culture [right(7C, 7F)]. The cells were taken at day 4 (7A, 7B, 7C) or day 6 (7D, 7E,7F), so that the released cells were analyzed at day 5 and day 7. Thecells were stained with no primary mAb [no 1ry], or with mAb togranulocytes [RB-6] or MHC class II products [B21-2] followed byFITC-mouse anti-rat Ig.

FIG. 8. FIGS. 8A through 8E are detailed cell cytofluorometric phenotypeanalyses of the Ia-positive cells released from the growing dendriticcell aggregates. Contaminating, Ia-negative granulocytes were gated outon the basis of lower forward light scatter, so that one could examinethe expression of many surface antigens on the larger cells using rat(FIGS. 8A through 8D) and hamster anti-mouse mAbs (7, 17) (FIG. 8E) asindicated.

FIG. 9. Quantitation of developing cells that bear the dendritic cellrestricted granule antigens 2A1 and M342.

Dendritic cells contain intracellular granules that react with the mAbsuch as M342 and 2A1 (34) mAbs. Ia-negative nonlymphocytes from mousemarrow were cultured in GM-CSF, and the loosely adherent granulocytesrinsed away at d2 and d4. The data on day 2 and 4 represent cells thatcould be dislodged by pipetting, while the data on d3 and d5-8 werecells released from the monolayer. At each of the indicated time points,at least 500 cells were counted in cytospins prepared and stained. [Seetext]. When cultures are started at 5×10⁵ cells/cm² and fed with ¾volume fresh medium every 2 days, the yields of total and Ia⁺ cells wereat d2, 1.05×10⁶ and 2.1×10⁴, at d4 1.81×10⁶ and 2.12×10⁵, and at d6,1.54×10⁶ and 3.21×10⁵.

FIG. 10. Progenitor-progeny relationships in growing dendritic cells.Growing aggregates were separated at d4 from bone marrow cultures andpulsed with ³H-TdR at 0.1 μCi/ml, 3×10⁵ cells/well, for 12 h. All wellswere replaced with fresh medium and returned to culture for 1, 2, or 3days of chase. The yields of released cells during the chase were 2.0,2.9, and 3.0×10⁵ respectively per well. The content of Ia⁺ cells was 28%after the pulse, and 47%, 55%, and 62% on days 1, 2, and 3 respectively.The data are shown as percentage of cells that were radiolabeled, withthe filled in bars being cells that express the 2A1 granule cell antigenof mature dendritic cells.

FIG. 11. Diagram of the proposed pathway of dendritic cell developmentin marrow cultures supplemented with GM-CSF. A proliferating aggregateforms from a precursor that either attaches to the cell stroma or isitself adherent. During dendritic cell differentiation, which is evidentat the periphery of the aggregate and in cells released therefrom, thereis a progressive increase in cell processes, MHC class II, NLDC-145surface antigen, and M342 and 2A1 intracellular antigen [see text] and aprogressive decrease in adherence to plastic.

FIG. 12. (FIGS. 12A-12D) Diff-Quick stains of developing dendritic cellsthat have been exposed to latex and carbon.

12A. An aggregate of developing dendritic cells cytospun after a 20 hexposure to 2 u latex spheres. Many cells in the aggregate are labeledwith the uniform latex particles [arrows].

12B. Same as A, but the cultures were chased for a day to allow theproduction of mature single dendritic cells.

Many of the released dendritic cells contain the uniform and lucentlatex spheres arranged around a clear cut centrosphere [arrows].

12C. Same as A and B, but the aggregates were pulsed with colloidalcarbon and then chased for a day in carbon-free medium. The centrosphereof some of the mature dendritic cells that release from the aggregatecontain small but clear cut endocytic granules of black, indigestiblephagocytic tracer [arrows].

12D. Mature dendritic cells were exposed to carbon after they had beenproduced from proliferating aggregates. Carbon deposits are not evident.

FIG. 13. (FIGS. 13A-13D) Uptake of BCG into developing dendritic cellsusing two-color labels for acid fast bacilli and dendritic cellantigens. Clusters of developing dendritic cells [6d marrow culturesinduced with GM-CSF] were exposed for 20 h to BCG. The monolayers werewashed and chased in medium with GM-CSF for 2d. The cells weredissociated, labeled with FITC-anti-I-A mAb, and the class II-rich cellswere isolated by cell sorting [most of the cells in the culture areclass II-rich as shown previously (16)]. The sorted cells were cytospun,stained with auramine-rhodamine to visualize the cell-associated BCG,and double labeled with a different mAb and immunoperoxidase. The leftand right panels of each pair are phase contrast (FIGS. 13A and 13C) andacid fast (FIGS. 13B and 13D) views respectively. Arrows on the leftindicate the location of the bacilli on the right. The label for classII, [I-A and I-E, M5/114] outlines the cell processes better than thedendritic cell-restricted NLDC-145 antibody.

FIG. 14. (FIGS. 14A-14D) Electron microscopy of BCG in dendritic cells.

As in FIG. 2, BCG was added to GM-CSF stimulated d6 bone marrow culturesfor a day. After washing and 2 more days of culture, the released cellswere processed for electron microscopy.

14A (X 5,400), 14B (X 3,100). Low power views to show the typicaldendritic cells with numerous processes and a few phagocytosed BCG[arrows].

14C (X 20,000), 14D (X 15,000). Higher power views to show phagosomalmembranes against the BCG, as well as organelles of the dendritic cellcentrosphere including endocytic vacuoles [E], Golgi apparatus [GA], andsmall vesicles with a dense core [*].

FIG. 15. Antigen presentation to CFA primed (FIG. 15A)/IFA (FIG. 15B)primed T cells.

T cells were purified from lymph nodes that drain paws that had beenprimed with complete [CFA] or incomplete [IFA] Freunds adjuvant. Thedifferent APCs are listed. Mature dendritic cells are d8 bone marrowcultures, and immature dendritic cells are from d5-6 cultures.

FIG. 16. Antigen presentation to naive lymph node T cells in situ.

Growing cultures of bone marrow dendritic cells were pulsed with BCG atd5-6, and used immediately or after a 2d chase culture to activate Tcells. The populations were injected into the paws of naive mice withoutartificial adjuvants. Five days later the draining lymph nodes weretaken and stimulated in vitro with graded doses of PPD or BSA (thedendritic cells had been grown with fetal calf serum), the BSA to serveas a nonparticulate antigen. Data are means and standard errors forgroups of 5 mice, each studied separately. Control lymph nodes notexposed to BCG pulsed dendritic cells did not respond to PPD or to BSA(<2000 cpm).

FIG. 17. (FIGS. 17A-17C) Antigen presentation to naive spleen cells insitu.

Growing cultures of bone marrow dendritic cells were pulsed with BCG atd5-6 (immature), at d7-8 (mature), or at d5-6 followed by a 2d chase.10⁶ cells of each group were injected i.v. into groups of mice. 5 or 10days later, the spleen cells were cultured in vitro with graded doses ofPPD (17A and 17C) or BSA (17B) as antigen. Since the dendritic cellswere cultured in FCS, the use of BSA serves as control to ensure thatall dendritic cell populations were comparably immunogenic in vivo.Unprimed spleen did not respond to either BSA or PPD.

FIGS. 18A, 18B and 18C. Mixed Leukocyte Reaction (MLR) assay of humandendritic cells produced according to the method described in Example 6.Graded doses of irradiated cells (30 to 30,000 in serial 3 folddilutions) were added to 2×10⁵ accessory cell-depleted T cells. The Tcell response of cells that had been cultured the absence of addedcytokine (X); and in the presence of GM-CSF (◯); GM-CSF+IL-1α ();GM-CSF+TNF-α (□); GM-CSF+TNF-α+IL-1α (▪); GM-CSF+IL-3 (Δ); andGM-CSF+IL-3+IL-1 (▴) was measured with a 16 h pulse of ³H-thymidine onthe 5th day. The response of non-dendritic cells is also shown in C,(♦). Three different experiments, shown in FIGS. 18A, 18B, and 18C arepresented. Patients providing cells for experiments A & B werepretreated with G-CSF; patient in experiment C was pretreated withGM-CSF. Cytokines were used at the following concentrations: rhu GM-CSF,400 or 800 U/ml; rhu IL-1α, 50 LAF units/ml (IL-1α was present incultures only during the last 24 hours prior to harvesting the cells);rhu TNF-α 50 U/ml; and rhu IL-3 100 U/ml. The values on the X axisrepresent the number of dendritic cells except for X where dendriticcells were absent and the number is equivalent to total cell number.Standard deviations of triplicate cultures were <10% of the mean, andare not shown.

FIG. 19. FIG. 19 comprises FIGS. 19A through 19E which shows developmentof DCs in liquid cultures of cord blood mononuclear cells supplementedwith GM-CSF and TNF. After 6d small adherent aggregates are visibleunder the inverted phase contrast microscope (19A). Higher magnificationreveals that they display typical veils at their edges (white arrows),and are affixed to adherent spindle-shaped cells (19B). At d14 the DCaggregates have become much larger (19C), and then finally releasetypical single DCs which display many processes (19D, bright field),notably characteristic veils (arrow indicates one such veil that appearsen face) (19E, phase contrast). 19A, 19C, ×25; 19B, ×100; 19D, 19E,×350.

FIG. 20. FIG. 20 comprises FIGS. 20A through 20F and shows T cellstimulatory function (1° allogeneic MLR) of dendritic cells (DC) grownfrom cord blood with GM-CSF+TNF α (20A), DC grown with GM-CSF+TNF fromblood of cancer patients after high-dose chemotherapy and G-CSFtreatment (20B), and DC grown from normal peripheral blood withGM-CSF+TNF α (20C) or with GM-CSF+IL-4 (20D, 20E, 20F). Responder cellswere purified T lymphocytes (2×10⁵ in 96 flat bottom wells). Equalnumbers of irradiated (3000 rad, ¹³⁷Cs) blood DC (closed circles in allpanels) as identified by FACS analyses (CD1a⁺/HLA-DR⁺ cells, compareFIG. 23) were compared both to cultured epidermal Langerhans cells [LC]from the same donor in 20D and to poorly stimulating cell populations(whole PBMC in 20D, and 20E; adherent macrophages from the same culturesin 20C; control cultures grown in the absence of cytokines in 20F [opentriangles]). Note that DC are 10-50-fold stronger than PBMC (20D, 20E)or macrophages (20C) and that they are comparable to DC from skin (20D).In addition, 20B and 20E show the enhancing effect of IL-1 (added duringthe last 24 h of culture) on the T cell stimulatory capacity of DC.Without cytokines no immunostimulatory DC develop in the cultures (20F).

FIG. 21. FIG. 21 comprises FIGS. 21A through 21C which shows developmentof DCs in liquid cultures of normal, adult blood mononuclear cellssupplemented with GM-CSF+IL-4. On d2.5 small adherent DC aggregates arereadily visible under the inverted phase contrast microscope (21A). Ond7 the DC aggregates have become nonadherent, very large, and loose(21B). The nonadherent fraction of the cultures was harvested andvigorously resuspended to obtain single DCs in large numbers (21C,arrows mark some veils). 21A, 21B, ×25; 21C, ×500.

FIG. 22. FIG. 22 comprises FIGS. 22A through 22D and shows phenotype andproliferation characteristics of DCs grown from normal blood withGM-CSF+IL-4. Fluorescence pictures in each row represent identicalmicroscopic fields of double-labeled cytospin preparations. Left panelsare stained with anti-HLA-DR. DC grown in GM-CSF and IL-4 are stronglyHLA-DR positive (22A, left) but display only a dull spot of anti-CD68reactivity (22A right). In contrast, control cells grown in parallelwithout cytokines (mainly macrophages) show an inverted pattern: verylow HLA-DR (22B, left) but brilliant CD68 expression (22B, right). MAbLag (22C, right) identifies occasional Birbeck granule containing cellsin the center of an HLA-DR-expressing aggregate of DC (22C, left).Peroxidase staining of nuclei and nucleoli with mAb Ki-67 (22D)demonstrates that proliferation occurs predominantly in aggregates (22D,left); singly dispersed DC derived from firmly adherent cells (see text)are not stained (22D, right). 22A-22C, ×200; 22D, ×100.

FIG. 23 Cytofluorographic analysis of dendritic cells (DC) grown fromnormal peripheral blood with GM-CSF+IL-4. Two different representativeexperiments are shown. Epidermal Langerhans cells (LC) cultured for 3dwere included in one experiment for comparison. Three colorimmunolabeling was performed. Cells were stained with different mousemAb's followed in sequence by biotinylated anti-mouse Ig,streptavidin-phycoerythrin, mouse Ig for blocking free binding sites,and FITC-conjugated anti-HLA-DR. Dead cells and lymphocytes wereexcluded from analysis by propidium iodide staining and light scatterproperties, respectively. More than 90% of the remaining cells werestrongly MHC-class II positive and constituted DC. The phenotype of thispopulation is shown here (shaded curves). Isotype-matched controlantibodies are included in each histogram (bold curves). Blood DCdisplay a phenotype typical for DC as described and almost identical tocultured LC in direct comparison (Lenz, et al. (1993). J. Clin. Invest.,92:2587; Freudenthal, P. S. and R. M. Steinman. (1990) Proc. Natl. Acad.Sci. USA., 87:7698; Romani, et al. (1989) J. Invest. Dermatol., 93:600;O'Doherty, et al. (1993) J. Exp. Med., 178:1067. Notably, they do notexpress CD14 but have high levels of MHC molecules (HLA-ABC, DR, DQ,DP), adhesions (CD54, CD58, CD11a*, CD11c), and costimulatory molecules(CD40, B7/CD80). They are also negative with markers for granulocytes(CD15), NK cells (CD16), B cells (CD19*, CD20), and T cells (CD3, CD8*).Expression of CD5 and the staining pattern of CD45RA and -RO are asdescribed for DC isolated from fresh blood O'Doherty, et al. (1993) J.Exp. Med., 178:1067 (34).

* not shown here.

FIG. 24. Ultrastructure of DCs grown from normal, adult bloodmononuclear cells with GM-CSF+IL-4. Low power view (×4,700) shows threeprofiles of DCs. Arrowheads indicate veils, i.e. thin cytoplasmicprocesses devoid of organelles. Area marked by bracket is shown athigher magnification (×33,000) to demonstrate the characteristicabundance of mitochondria and paucity of lysosomes/phagosomes.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a method of producing cultures ofproliferating dendritic cell precursors which mature in vitro to maturedendritic cells. The dendritic cells and the dendritic cell precursorsproduced according to the method of the invention may be produced inamounts suitable for various immunological interventions for theprevention and treatment of disease.

The starting material for the method of producing dendritic cellprecursors and mature dendritic cells is a tissue source comprisingdendritic cell precursors which precursor cells are capable ofproliferating and maturing in vitro into dendritic cells when treatedaccording to the method of the invention. Such precursor cells arenonadherent and typically do not label with mAb markers found on maturedendritic cells such as Ia antigens, 2A1 and M342 antigens (34, 44) andthe NLDC145 interdigitating cell source antigen (13). Preferably suchtissue sources are spleen, afferent lymph, bone marrow and blood. Morepreferred tissue sources are bone marrow and blood. Blood is also apreferred tissue source of precursor cells because it is easilyaccessible and could be obtained in relatively large quantities.

To increase the number of dendritic precursor cells in animals,including humans it is preferable to treat such individuals withsubstances which stimulate hematopoiesis. Such substances include G-CSF,GM-CSF and may include other factors which promote hematopoiesis. Theamount of hematopoietic factor to be administered may be determined byone skilled in the art by monitoring the cell differential ofindividuals to whom the factor is being administered. Typically, dosagesof factors such as G-CSF and GM-CSF will be similar to the dosage usedto treat individuals recovering from treatment with cytotoxic agents.Preferably, GM-CSF or G-CSF is administered for 4 to 7 days at standarddoses prior to removal of source tissue to increase the proportion ofdendritic cell precursors. (Editorial, Lancet, 339: Mar. 14, 1992,648-649). For example, we have determined that dosages of G-CSF of 300micrograms daily for 5 to 13 days and dosages of GM-CSF of 400micrograms daily for 4 to 19 days have resulted in significant yields ofdendritic cells.

Fetal or umbilical cord blood, which is also rich in growth factors isalso a preferred source of blood for obtaining precursor dendriticcells.

According to a method of the invention, the tissue source may be treatedprior to culturing to enrich the proportion of dendritic precursor cellsrelative to other cell types. Such pretreatment may also remove cellswhich may compete with the proliferation of dendritic precursor cells orinhibit their proliferation or survival. Pretreatment may also be usedto make the tissue source more suitable for in vitro culture. The methodof treatment will likely be tissue specific depending on the particulartissue source. For example, spleen or bone marrow if used as a tissuesource would first be treated so as to obtain single cells followed bysuitable cell separation techniques to separate leukocytes from othercell types. Treatment of blood would involve cell separation techniquesto separate leukocytes from other cells types including red blood cells(RBCs) which are toxic. Removal of RBCs may be accomplished by standardmethods known to those skilled in the art. In addition, antitoxins suchas anti-erythroid monoclonal VIE-64 antibody which bind RBCs may be usedto facilitate binding of RBC to a substrate for removal using a panningtechnique.

According to a preferred method of this invention, when bone marrow isused as the tissue source, B cells are removed prior to culturing ofbone marrow in GM-CSF. While B cells and pre-B cells do not grow inresponse to GM-CSF, they represent approximately 50% of the initialmarrow suspension and thereby preclude the use of staining with anti-Iamonoclonal antibodies to quickly enumerate dendritic cells.Additionally, granulocytes are GM-CSF responsive and readily proliferatein the presence of GM-CSF. As such, the B cells and granulocytes maskthe presence of dendritic cell precursors. B cells can express the M342and 2A1 granular antigens that are useful markers for distinguishingdendritic cells from macrophages and granulocytes. Moreover,granulocytes have a tendency to overgrow the cultures and compete foravailable GM-CSF. The most preferred method under this invention is toremove the majority of nonadherent, newly-formed granulocytes from thebone marrow cultures by gentle washes during the first 2-4 days inculture.

Preferably, in one form of pretreatment cells which compete and mask theproliferation of precursor dendritic cells are killed. Such pretreatmentcomprises killing cells expressing antigens which are not expressed ondendritic precursor cells by contacting bone marrow with antibodiesspecific for antigens not present on dendritic precursor cells in amedium comprising complement. Another form of pretreatment to removeundesirable cells suitable for use with this invention is adsorbing theundesirable precursor cells or their precursors onto a solid supportusing antibodies specific for antigens expressed on the undesirablecells. Several methods of adsorbing cells to solid supports of varioustypes are known to those skilled in the art and are suitable for usewith this invention. For example, undesirable cells may be removed by“panning” using a plastic surface such as a petri dish. Alternatively,other methods which are among those suitable include adsorbing cellsonto magnetic heads to be separated by a magnetic force; or immunobeadsto be separated by gravity. Non adsorbed cells containing an increasedproportion of dendritic cell precursors may then be separated from thecells adsorbed to the solid support by known means including panning.These pretreatment step serves a dual purpose: they destroy or revivesthe precursors of non-dendritic cells in the culture while increasingthe proportion of dendritic cell precursors competing for GM-CSF in theculture.

In addition, Ia-positive cells, i.e. B cells and macrophages preferablyare killed by culturing the cells in the presence of a mixture of antiIa-antibodies, preferably monoclonal antibodies, and complement. Maturedendritic cells which are also present in bone marrow are also killedwhen the cells from the bone marrow are cultured in the presence of antiIa-antibodies, however, these mature dendritic cells occur in such lowquantities in the blood and bone marrow and possess such distinctantigenic markers from dendritic cell precursors that killing of thesemature dendritic cells will not significantly effect the proliferationand yield of dendritic cell precursors. T and B cells as well asmonocytes which also may be present in the bone marrow may be killed byincluding antibodies directed against T and B cell antigens andmonocytes. Such antigens include but are not limited to CD3, CD4, the Bcell antigen B220, thy-1, CD8 and monocyte antigens. The remainingviable cells from the bone marrow are then cultured in mediumsupplemented with about 500-1000 U/ml GM-CSF and cultured as describedbelow. It should be noted that CD4 and CD8 antigens may be present onyoung dendritic cell precursors, therefore, antibodies directed to theseantigens may deplete the dendritic cell precursor populations.

When blood is used as a tissue source, blood leukocytes may be obtainedusing conventional methods which maintain their viability. According tothe preferred method of the invention, blood is diluted into medium(preferably RPMI) containing heparin (about 100 U/ml) or other suitableanticoagulant. The volume of blood to medium is about 1 to 1. Cells arepelleted and washed by centrifugation of the blood in medium at about1000 rpm (150 g) at 4° C. Platelets and red blood cells are depleted bysuspending the cell pellet in a mixture of medium and ammonium chloride.Preferably the mixture of medium to ammonium chloride (finalconcentration 0.839 percent) is about 1:1 by volume. Cells are pelletedby centrifugation and washed about 2 more times in the medium-ammoniumchloride mixture, or until a population of leukocytes, substantiallyfree of platelets and red blood cells, is obtained.

Any isotonic solution commonly used in tissue culture may be used as themedium for separating blood leukocytes from platelets and red bloodcells. Examples of such isotonic solutions are phosphate bufferedsaline, Hanks balanced salt solution, or complete growth mediumsincluding for example RPMI 1640. RPMI 1640 is preferred.

Cells obtained from treatment of the tissue source are cultured to forma primary culture on an appropriate substrate in a culture mediumsupplemented with GM-CSF or a GM-CSF derivative protein or peptidehaving an amino acid sequence which sequence maintains biologic activitytypical of GM-CSF. The appropriate substrate may be any tissue culturecompatible surface to which cells may adhere. Preferably, the substrateis commercial plastic treated for use in tissue culture. Examplesinclude various flasks, roller bottles, petri dishes and multi-wellcontaining plates made for use in tissue culture. Surfaces treated witha substance, for example collagen or poly-L-lysine, or antibodiesspecific for a particular cell type to promote cell adhesion may also beused provided they allow for the differential attachment of cells asdescribed below. Cells are preferably plated at an initial cell densityof about 7.5×10⁵ cells per cm². At this dose, the surface is not fullycovered by cells, but there are no big spaces (2-3 cell diameters)either.

When bone marrow which has been treated to reduce the proportion ofnon-dendritic cell precursors is cultured, aggregates comprisingproliferating dendritic cell precursors are formed. The Ia-negativemarrow nonlymphocytes comprising dendritic cell precursors arepreferably cultured in high numbers, about 10⁶/well (5×10⁵ cells/cm²)Liquid marrow cultures which are set up for purposes other thanculturing dendritic cell precursors are typically seeded at 1/10th thisdose, but it is then difficult to identify and isolate the aggregates ofdeveloping dendritic cells.

The growth medium for the cells at each step of the method of theinvention should allow for the survival and proliferation of theprecursor dendritic cells. Any growth medium, typically used to culturecells may be used according to the method of the invention provided themedium is supplemented with GM-CSF. Preferred medias include RPMI 1640,DMEM and α-MEM, with added amino acids and vitamins supplemented with anappropriate amount of serum or a defined set of hormones and an amountof GM-CSF sufficient to promote proliferation of dendritic precursorcells. Serum-free medium supplemented with hormones is also suitable forculturing the dendritic cell precursors. RPMI 1640 supplemented with 5%fetal calf serum (FCS) and GM-CSF is preferred. Cells may be selected oradapted to grow in other serums and at other concentrations of serum.Cells from human tissue may also be cultured in medium supplemented withhuman serum rather than FCS. Medias may contain antibiotics to minimizebacteria infection of the cultures. Penicillin, streptomycin orgentamicin or combinations containing them are preferred. The medium, ora portion of the medium, in which the cells are cultured should beperiodically replenished to provide fresh nutrients including GM-CSF.

GM-CSF has surprisingly been found to promote the proliferation in vitroof precursor dendritic cells. Cells are cultured in the presence ofGM-CSF at a concentration sufficient to promote the survival andproliferation of dendritic cell precursors. The dose depends on theamount of competition from other cells (especially macrophages andgranulocytes) for the GM-CSF, or to the presence of GM-CSF inactivatorsin the cell population. Preferably, the cells are cultured in thepresence of between about 1 and 1000 U/ml of GM-CSF. More preferablycells from blood are cultured in the presence of GM-CSF at aconcentration of between about 30 and 100 U/ml. This dose has been foundto be necessary and sufficient for maximal responses by cells obtainedfrom mouse blood. Most preferably, cells are cultured in the presence ofGM-CSF at a concentration of about 30 U/ml. GM-CSF at a concentration ofbetween about 400-800 U/ml has been found to be optimal for culturingproliferating human dendritic cells from blood. Cells from bone marrowrequire higher concentrations of GM-CSF because of the presence of largenumbers of proliferating granulocytes which compete for the availableGM-CSF, therefore, doses between about 500-1000 U/ml are preferred forcultures of cells obtained from marrow.

When suspensions of mouse bone marrow are cultured in the presence ofGM-CSF, three types of myeloid cells expand in numbers. (1) Neutrophilspredominate but do not adhere to the culture surface. Neutrophils have acharacteristic nuclear morphology, express the RB-6 antigen, and lackMHC class II products. (2) Macrophages are firmly adherent to theculture vessel, express substantial levels of the F4/80 antigen, and forthe most part express little or no MHC class II [but see below].

When mouse or human blood leukocytes are cultured in GM-CSF at 30 U/mlor 400-800 U/ml, respectively, the cultures develop a large number ofaggregates or cell balls from which typical dendritic cells areeventually released. In the absence of GM-CSF, no colonies develop.Cytologic criteria may be used to initially detect the dendritic cellswhich characteristically extend large, sheet-like processes or veils(25-27).

GM-CSF may be isolated from natural sources, produced using recombinantDNA techniques or prepared by chemical synthesis. As used herein, GM-CSFincludes GM-CSF produced by any method and from any species. “GM-CSF” isdefined herein as any bioactive analog, fragment or derivative of thenaturally occurring (native) GM-CSF. Such fragments or derivative formsof GM-CSF should also promote the proliferation in culture of dendriticcell precursors. In addition GM-CSF peptides having biologic activitycan be identified by their ability to bind GM-CSF receptors onappropriate cell types.

It may be desirable to include additional cytokines in the culturemedium in addition to GM-CSF to further increase the yield of dendriticcells. Such cytokines include granulocyte colony-stimulating factor(G-CSF), monocyte-macrophage colony-stimulating factor (M-CSF),interleukins 1α and 1β, 3, 4, 6, and 13 (IL-1α, IL-1β, IL-3, IL-4, IL-6,and IL-13 respectively), tumor necrosis factor α (TNFα), and stem cellfactor (SCF). Cytokines are used in amounts which are effective inincreasing the proportion of dendritic cells present in the cultureeither by enhancing proliferation or survival of dendritic cellprecursors. Preferably, cytokines are present in the followingconcentrations: IL-1α and β, 1 to 100 LAF units/ml; TNF-α, 5-500 U/ml;IL-3, 25-500 U/ml; M-CSF, 100-1000 U/ml; G-CSF, 25-300 U/ml; SCF, 10-100ng/ml; IL-4, 500-1000 U/ml and IL-6, 10-100 ng/ml. More preferredconcentrations of cytokines are: IL-1α, 50 LAF units/ml; TNFα, 50 U/ml;IL-3, 100 U/ml; M-CSF, 300 U/ml; and G-CSF, 100 U/ml. Preferredcytokines are human proteins. Most preferred cytokines are produced fromthe human gene using recombinant techniques (rhu). (TNFα) atconcentrations from about 10-50 U/ml may be used to increase dendriticcell yields several fold.

In certain tissue sources the presence of non-dendritic cell precursorsor stem cells capable of maturing to non-dendritic cells may reduce theproportion of mature dendritic cells obtained. It may therefore bedesirable to reduce the population of non-dendritic cells present in theculture by including factors which inhibit the proliferation ormaturation of non-dendritic cell precursors. For example, if human bloodisolated from healthy humans is the tissue source for dendriticprecursors it is preferred that isolated peripheral blood mononuclearcells are cultured in GM-CSF and at least one additional agent. Thisagent should inhibit the proliferation and/or maturation of other celltypes within the culture. It is preferable that such an agent inhibitmacrophage proliferation and/or maturation without substantiallyinhibiting dendritic cell proliferation and/or maturation. Examples ofsuch a macrophage inhibiting agent includes, but are not limited to,IL-4 and IL-13. A suggested range for IL-4 is 500-1000 U/ml. It ispreferred that the IL-4 be present at the start or immediatelythereafter of the culture. The IL-4 may be isolated from natural sourcesor recombinantly produced.

Without being bound by theory the TNF-α may facilitate the proliferationof dendritic progenitors present in human cord blood and human bloodisolated from chemotherapeutic patients pretreated with GM-CSF but doesnot enhance proliferation of many dendritic precursors present in normalhuman blood.

GM-CSF, however is essential for the proliferation and maturation ofdendritic cell precursors.

TNF-α appears to facilitate the proliferation of dendritic cellprogenitors cultured in GM-CSF found in cord blood (Caux et al Nature(1992) 360:258-261; example 8 and blood isolated from chemotherapeuticpatients pretreated with GM-CSF). However TNF-α does not appear tofacilitate dendritic cell proliferation in many dendritic cellprogenitors isolated from normal human blood and cultured in GM-CSF (seeexample 8).

TNF-α may, however negatively impact on antigen retention andpresentation in non-proliferating dendritic cells. In another embodimentof this invention proliferating dendritic cell are cultured in thepresence of GM-CSF and TNF-α at a time sufficient to allow increasedproliferation of the dendritic cell progenitors without impairing theantigen presenting and retention abilities of the dendritic cell.

The primary cultures from the tissue source are allowed to incubate atabout 37° C. under standard tissue culture conditions of humidity and pHuntil a population of cells has adhered to the substrate sufficiently toallow for the separation of nonadherent cells. The dendritic cellprecursor in blood initially is nonadherent to plastic, in contrast tomonocytes, so that the precursors can be separated after overnightculture. Monocytes and fibroblasts are believed to comprise the majorityof adherent cells and usually adhere to the substrate within about 6 toabout 24 hours. Preferably nonadherent cells are separated from adherentcells between about 8 to 16 hours. Most preferably nonadherent cells areseparated at about 12 hours. Any method which does not dislodgesignificant quantities of adherent cells may be used to separate theadherent from nonadherent cells. Preferably, the cells are dislodged bysimple shaking or pipetting. Pipetting is most preferred.

To culture precursor cells from human blood from this primary culture,cells which have been depleted of cells that are not dendritic cellprecursors are cultured on a substrate at a density of preferably about5×10⁵ cells per cm². After 5 days, with feedings every other day, cellaggregates appear (also referred to as “balls”). These aggregates maythen be treated as described below.

The nonadherent cells from the primary culture are subcultured bytransferring them to new culture flasks at a density sufficient to allowfor survival of the cells and which results in the development over timeof clusters of growing cells that are loosely attached to the culturesurface or to the firmly adherent cells on the surface. These clustersare the nidus of proliferating dendritic cell precursors. As used herein“culture flasks” refers to any vessel suitable for culturing cells. Itis desirable to subculture all of the nonadherent cells from the primaryculture at a density of between about 2×10⁵ cells and 5×10⁵ cells percm². Preferably at about 2.5×10⁵ per cm². Cells are incubated for asufficient time to allow the surface of the culture dish to becomecovered with a monolayer of tightly adherent cells including macrophagesand fibroblasts affixed to which are aggregates of nonadherent cells. Atthis time, any nonadherent cells are removed from the wells, and thecellular aggregates are dislodged for subculturing. Preferably the cellsfrom the aggregates are subcultured after about 10 days or when thenumber of aggregated cells per cm² reaches about 3 to 4×10⁵.

For serially subculturing the aggregated cells, the aggregated cells aredislodged from the adherent cells and the aggregated cells aresubcultured on a total surface area of preferably between about 2 to 5times that of the surface area of the parent culture. More preferablythe cells are subcultured on a surface area that is about 3 times thesurface area of the parent culture. Cells having sheet-like processestypical of dendritic cells appear in the culture at about 4-7 days.Between about day 10 and day 17 of culture the number of single cellsthat can be recovered from a given surface area doubles. Both dendriticcell precursors and mature dendritic cells are present in theaggregates.

For producing dendritic cell from bone marrow, preferably thedistinctive aggregates of proliferating, less mature dendritic cells areseparated away from the stroma at about after about 4-6d of culture.Large numbers of dendritic cells are released and it is this releasedpopulation that expresses the cardinal features of mature dendriticcells. Because bone marrow initially contains a greater proportion ofdendritic cell precursors than blood, only about 4-6 days of culture ofthe cells obtained from bone marrow are necessary to achieve about thesame number of cells which are obtained after about 10 to 25 days ofculture of cells obtained from blood.

To further expand the blood derived population of dendritic cells, cellaggregates may be serially subcultured multiple times at intervals whichprovide for the continued proliferation of dendritic cell precursors.Preferably, aggregates are subcultured prior to the release into themedium of a majority of cells having the dendritic cell morphology, forexample between about 3 and 30 days. More preferably aggregates of cellsare subcultured between about 10 to 25 days in culture, and mostpreferably at 20 days. The number of times the cells are seriallysubcultured depends on the number of cells desired, the viability of thecells, and the capacity of the cultures to continue to produce cellaggregates from which dendritic cells are released. Preferably, cellscan be serially subcultured for between about 1 to 2 months from whenthe nonadherent cells were subcultured or between about one to fivetimes. More preferably cells are serially subcultured about two to threetimes. Most preferably cells are serially subcultured twice.

According to a preferred method, to serially subculture the cells of theprimary and subsequent cultures, cells are dislodged by pipetting mostof the aggregates of growing dendritic cells as well as some cells inthe monolayer of growing macrophages and fibroblasts. Pipetting usuallydisrupts the aggregates, particularly the peripheral cells of theaggregates which are more mature. With time in culture, e.g., at 2weeks, the aggregates of the growing dendritic cells become more stableand it is possible to dislodge the aggregates for separation by 1 gsedimentation.

Alternative approaches may be used to isolate the mature dendritic cellsfrom the growing cultures. One is to remove cells that are nonadherentand separate the aggregates from cells attached to substrate and singlecells by 1 g sedimentation. Dendritic cells are then released in largenumbers from the aggregates over an additional 1-2 days of culture,while any mature dendritic cells can be isolated from other single cellsby floatation on dense metrizamide as described (Freudenthal andSteinman, Proc. Natl. Acad. Sci. USA 87:7698-7702, 1990). The secondmethod, which is simpler but essentially terminates the growth phase ofthe procedure, is to harvest all the nonadherent cells when theaggregates are very large, leave the cells on ice for about 20 minutes,resuspend vigorously with a pipette to disaggregate the aggregates andfloat the mature dendritic cells on metrizamide columns.

Typically the contents of five 16 mm wells are applied to a 6 ml columnof 50% FCS-RPMI 1640 in a 15 ml conical tube [Sarstedt, 62.553.002 PS].After at least 20 min, the applied medium and top 1 ml of the column areremoved. RPMI is added, the aggregates are pelleted at 1000 rpm at 4°for 5 min, and the cells are suspended gently for subculture in freshmedium.

Various techniques may be used to identify the cells present in thecultures. These techniques may include analysis of morphology, detectingcell type specific antigens with monoclonal antibodies, identifyingproliferating cells using tritiated thymidine autoradiography, assayingmixed leukocyte reactions, and demonstrating dendritic cell homing.

The dendritic cells besides being identified by their stellate shape mayalso be identified by detecting their expression of specific antigensusing monoclonal antibodies.

A panel of monoclonal antibodies may be used to identify andcharacterize the cells in the GM-CSF expanded cultures. The monoclonalantibodies are reviewed elsewhere (23, 24 which are incorporated hereinby reference).

Among the specific monoclonal antibodies suitable for identifying maturedendritic cells are: 1) those which bind to the MHC class I antigen(M1/42 anti-MHC class I [ATCC #TIB 126]); 2) those which bind to the MHCclass II antigen (B21-2 anti-MHC class II [ATCC #TIB 229]; M5/114anti-MHC class II [ATCC #TIB 120]); 3) those which bind to heat stableantigen (M1/69 anti-heat stable antigen [HSA, ATCC #T1B 125]); 4) 33D1anti-dendritic cell antibodies [ATCC #TIB 227]; 5) those which bind tothe interdigitating cell antigen (NLDC145 anti-interdigitating cell(13); and 6) those which bind to antigens in granules in the perinuclearregion of mature dendritic cells (monoclonal antibodies 2A1 and M342,(23) Agger et al.). Other antigens which are expressed by the dendriticcells of the invention and which may be used to identify maturedendritic cells are CD44 (identified with monoclonal antibody 2D2C), andCD11b (identified with monoclonal antibody M1/70. The M1/69, M1/70,M1/42 monoclonal antibodies are described in Monoclonal antibodies, NY,Plenum 1980, ed. R. Kennett et al. pages 185-217 which is incorporatedherein by reference. Those of skill in the art will recognize that otherantibodies may be made and characterized which are suitable foridentifying mature dendritic cells. Similarly, the production ofdendritic precursor cells also facilitates the production of antibodiesspecific for dendritic precursor cells.

To identify and phenotype the proliferating cells and their progeny,cultures may be labelled with tritiated thymidine to identify the cellsin the S phase of mitosis. In addition to labelling the cells with amitotic label, cells may also be co-labelled with monoclonal antibodiesto determine when markers associated with mature dendritic cells areexpressed. The distinctive phenotype of the dendritic cell precursors isstable so that for example, the dendritic cell progeny do not becomemacrophages even when maintained in macrophage colony stimulating factor(M-CSF).

Another index of dendritic cell maturity is the ability of maturedendritic cells to stimulate the proliferation of T-cells in the mixedleukocyte reaction (MLR). The ability of dendritic cells to migrate tolymph nodes, i.e., dendritic cell homing is another index of dendriticcell maturation which may be used to assess the maturity of the cells inculture.

The criteria that have become evident for identifying dendriticprecursor cells according to the invention enables the identification ofproliferating progenitors of dendritic cells in other organs. It isknown that proliferating precursors give rise to the rapidly turningover populations of dendritic cells in spleen (15) and afferent lymph(16). The proliferation of leukocytes [other than T cells] occurs in thebone marrow, but it may be that for dendritic cells, the marrow alsoseeds the blood and other tissues with progenitors which thenproliferate extensively as shown here. By being able to prepare theotherwise trace dendritic cell in large numbers according to the methodof this invention, other previously unexplored areas of dendritic cellfunction may now be determined. Specifically, growing dendritic cellswill facilitate molecular and clinical studies on the mechanism ofaction of these APCs, including their capacities to capture and retainantigens in an immunogenic form and act as adjuvants for the generationof immunity in vivo.

There is an increased interest in the use of constituent proteins andpeptides to modulate T cell responses to complex microbial and cellularantigens in situ. Typically artificial adjuvants such as alum arerequired to produce a maximum immunogenic effect. Several antigens areknown to be immunogenic when administered in association with dendriticcells but in the absence of additional adjuvants (1). The immunogenicityof dendritic cells in situ has been shown with for example contactallergens (45), transplantation antigens (46-49), and more recentlyforeign proteins (31, 50, 51). Other types of antigens include but arenot limited to microbial, tumor and viral antigens. Dendritic cellsserve directly as APCs in situ, because the T cells that are primed arerestricted to recognize only antigens presented by the particular MHCclass of the immunizing dendritic cells rather than host APCs (14, 31,50, 51). These observations, when coupled with data that dendritic cellsare efficient at capturing protein antigens in an immunogenic form insitu (52-54), allow these APCs to be considered “nature's adjuvant”.This invention therefore enables the utilization of dendritic cells bydisclosing methods and compositions suitable for providing sufficientquantities of dendritic cell precursors in order to take advantage oftheir unique antigen presenting capabilities in clinical and therapeuticpractices.

Dendritic cells are capable of processing complex antigens into thosepeptides that would be presented by self MHC products. Among thepreferred embodiments of our invention is a method for using dendriticcells whereby the dendritic cell precursors internalize particulatesduring an early stage in their development from proliferatingprogenitors. We have established that stimulation of bone marrowsuspensions with GM-CSF leads to the production of clusters ofproliferating dendritic cell precursors. The cells that pulse label with3H-thymidine in the clusters lack many of the characteristic markers ofdendritic cells, e.g., stellate shape and antigenic features likeNLDC-145 antigen and high levels of MHC class II. In pulse chaseexperiments, 3H-thymidine-labeled progeny with all the features ofdendritic cells are released. We have found that cells within theaggregate also are phagocytic, and that in analogous pulse chaseprotocols, the progeny dendritic cells are clearly labeled with thephagocytic meal. When the particles are BCG organisms such as thosecausing tuberculosis, mycobacterial antigens associated with thedendritic cells are presented in a potent manner to T cells in vitro andin situ.

Foreign and autoantigens are processed by the dendritic cells of theinvention to retain their immunogenic form. The immunogenic form of theantigen implies processing the antigen through fragmentation to producea form of the antigen that can be recognized by and stimulate T cells.Preferably, such foreign or autoantigens are proteins which areprocessed into peptides by the dendritic cells. The relevant peptideswhich are produced by the dendritic cells may be extracted and purifiedfor use as immunogens.

Peptides processed by the dendritic cells may also be used as toleragensto induce tolerance to the proteins processed by the dendritic cells ordendritic cell precursors. Preferably when used as toleragens, theprocessed peptides are presented on dendritic cells which have beentreated to reduce their capacity to provoke an immune response as byinhibiting their accessory function by blocking accessory molecules suchas B7 present on the dendritic cells.

The antigen-activated dendritic cells of the invention are produced byexposing antigen, in vitro, to the dendritic cells prepared according tothe method of the invention. Dendritic cells are plated in culturedishes and exposed to antigen in a sufficient amount and for asufficient period of time to allow the antigen to bind to the dendriticcells. The amount and time necessary to achieve binding of the antigento the dendritic cells may be determined by immunoassay or bindingassay. Other methods known to those of skill in the art may be used todetect the presence of antigen on the dendritic cells following theirexposure to antigen.

Without being bound by theory, the information at present suggests thatthe development of dendritic cells proceeds by the following pathway[FIG. 11]. The dendritic cell precursors in both blood and marrow lackMHC class II antigens as well as B and T cell and monocyte markers[B220, CD3, thy-1, CD4/8], and the precursors are nonadherent. Theprecursors attach to the stroma and give rise to aggregates of class IIpositive cells. Perhaps the growing aggregates arise from a subset ofstrongly class II-positive cells that are found in the firmly adherentmonolayer even at later time points. However, these firmly adherent,class II rich cells lack the MLR stimulatory activity of dendritic cellsand may express substantial levels of Fcγ receptors and the F4/80antigen. The final stage of development is that the loosely attachedaggregate releases mature, nonproliferating dendritic cells. The latterhave even higher levels of MHC class II [FIG. 2-3] and can attachtransiently to plastic, much like many of the dendritic cells releasedfrom spleen (25). As development occurs in the aggregate, there seems tobe a reduction in the levels of cytoplasmic staining for Fcγ receptorsand F4/80 antigen, and an increase in granule [M342, 2A1] and surfaceantigens [33D1, NLDC145] that are characteristic of dendritic cells.Lastly, accessory function for primary T-dependent immune responsesincreases as cells are released from the growing aggregates.

Mature dendritic cells, while effective in sensitizing T cells toseveral different antigens, show little or no phagocytic activity. Tothe extent that endocytosis is required for antigen processing andpresentation, it was not previously evident how dendritic cells wouldpresent particle-associated peptides. Based on our work, it is nowevident that progenitors to dendritic cells which this inventionprovides can internalize such particles for processing and presentation.The types of particles which may be internalized by phagocytosis includebacteria, viral, mycobacteria or other infectious agents capable ofcausing disease. Accordingly, any antigenic particle which isinternalized and processed by the dendritic cell precursors of thisinvention is also suitable for making the various immunogens, toleragensand vaccines described as part of this invention. Processing of antigenby dendritic cells or dendritic cell precursors includes thefragmentation of an antigen into antigen fragments which are thenpresented.

Phagocytoses of particulate matter by dendritic cell precursors may beaccomplished by culturing the dendritic cell precursors in the presenceof particulate matter for a time sufficient to allow the cells tophagocytose, process and present the antigen. Preferably, culturing ofthe cells in the presence of the particles should be for a period ofbetween 1 to 48 hours. More preferably, culturing cells in the presenceof particulate matter will be for about 20 hours. Those of skill in theart will recognize that the length of time necessary for a cell tophagocytose a particle will be dependent on the cell type and the natureof the particle being phagocytosed. Methods to monitor the extent ofsuch phagocytosis are well known to those skilled in the art.

Cells should be exposed to antigen for sufficient time to allow antigensto be internalized and presented on the cell surface. The time necessaryfor the cells to internalize and present the processed antigen may bedetermined using pulse-chase protocols in which exposure to antigen isfollowed by a wash-out period. Once the minimum time necessary for cellsto express processed antigen on their surface is determined, apulse-chase protocol may be used to prepare cells and antigens foreliciting immunogenic responses.

The phagocytic dendritic precursor cells are obtained by stimulatingcell cultures comprising dendritic precursor cells with GM-CSF to induceaggregates of growing dendritic cells. These dendritic precursor cellsmay be obtained from any of the source tissues containing dendritic cellprecursors described above. Preferably, the source tissue is bone marrowor blood cultures. Cells within these aggregates are clearly phagocytic.If the developing cultures are exposed to particles, washed and “chased”for 2 days, the number of MHC-class II rich dendritic cells increasessubstantially and at least 50% contain internalized particles such asBCG mycobacteria or latex particles. The mycobacteria-laden, newlydeveloped, dendritic cells are much more potent in presenting antigensto primed T cells than corresponding cultures of mature dendritic cellsthat are exposed to a pulse of organisms.

A similar situation pertains when BCG-charged, dendritic cells areinjected into the footpad or blood stream of naive mice. Those dendriticcells that have phagocytosed organisms induce the strongest T cellresponses to mycobacterial antigens in draining lymph node and spleen.The administration of antigens to GM-CSF induced, developing dendriticcells—by increasing both antigen uptake and cell numbers—will facilitatethe use of these APCs for active immunization in situ. The production ofsuch strong immunogenic responses due to the presentation of antigen bythe dendritic cells makes these cells and this system particularlydesirable as adjuvants useful for producing immunogenic responses inindividuals. Such immunogenic responses and the development ofantibodies to the presented antigens may be used to treat ongoinginfections or prevent future infections as with a vaccine. The use ofdendritic cells to produce a therapeutic or prophylactic immune responsein an individual may be particularly useful to treat or preventinfection by drug resistant organisms, such as, for example, the BCGmycobacterium causing tuberculosis.

Immunogenicity of ingested particles can be obtained with BCGmycobacteria (FIG. 12-13). In any inoculum of the BCG vaccine, there arelive bacilli [approximately 50% of the bacilli act as colony formingunits], dead bacilli, and probably a number of mycobacterial proteins.The phagocytosed pool of BCG is being presented to T cells by dendriticcells. This is evident after comparing the presentation of mycobacterialantigens with bovine serum albumin (BSA), a component of the serum inwhich the dendritic cells are grown. All the APC populations werecomparable in presenting BSA, but dendritic cells that had phagocytosedthe most BCG were the most effective APCs for mycobacteria (FIGS. 12 and13, ♦). BCG particle uptake, therefore, accounts for the bulk of themycobacterial priming by the dendritic cell precursors.

Another embodiment of this invention is therefore to pulse dendriticcell precursors with mycobacteria tuberculosis bacteria antigen,including for example BCG antigen, to induce host resistance tomycobacteria infection, a matter of importance given the need to developbetter vaccination and treatment protocols for tuberculosis, includingthe drug resistant variety (78).

In effect, the pulse and chase protocol which may be used to chargedeveloping dendritic cells with organisms according to our inventionallows the two broad components of immunostimulation to take placesequentially. These components are a) antigen capture and presentation,here the capture of particulates by immature dendritic cells, and b)development of potent accessory or immunostimulatory functions duringthe chase period. The situation is comparable to that seen in thehandling of soluble proteins (4, 6) and particles (74) by epidermalLangerhans cells. Each of the two broad components of APC functionentails many subcomponents. For example, immature dendritic cells notonly are more phagocytic but display other features needed for antigenpresentation such as active biosynthesis of abundant MHC class IImolecules and invariant chain (6, 7) and numerous acidic endocyticvacuoles (36).

The capacity to charge APCs with antigens using pulse chase protocolsmay be a special feature of dendritic cells. Prior studies withmacrophages and B cells had suggested that T cell epitopes areshort-lived (75). The results described here and elsewhere (6, 14, 71)indicates that immunogenic peptides can be long lived on dendritic cellsat least 2 days prior to injection into mice. This retention capacityshould enable dendritic cells to migrate and sensitize T cells indraining lymphoid tissues over a period of several days (14, 50, 51).

An important feature of the dendritic cells of this invention is thecapacity to efficiently present microbial and other antigens on bothclass I and II products. In the case of BCG, the bulk of the primedcells are CD4+ T cells, most likely because the antigenic load ishandled by the endocytic pathway and MHC class II products (76). In thecase of influenza, it has been found that the class I pathway forinducing CD8+ cytotoxic T lymphocytes (CTL) requires adequate deliveryof antigen (infectious virus) into the cytoplasm, whereas the purelyendocytic pathway delivers noninfectious virions for presentation onlyto CD4⁺ helpers (77). Developing dendritic cell cultures provides anopportunity for charging MHC class I products with peptide, since cellproliferation allows various methods of gene insertion (as withretroviral vectors) to be applied.

According to this further embodiment of the invention, the proliferatingdendritic cells may be injected with a vector which allows for theexpression of specific proteins by the dendritic cells. These viralproteins which are expressed by the dendritic cell may then be processedand presented on the cell surface on MHC I receptors. The viralantigen-presenting cells or the processed viral antigens themselves maythen be used as immunogens to produce an immunogenic response to theproteins coded by the vector.

Vectors may be prepared to include specific DNA sequences which code andexpress genes for proteins to which an immunogenic response is desired.Preferably, retroviral vectors are used to infect the dendritic cells.The use of retroviral vectors to infect host cells is known to thoseskilled in the art and is described in WO 92/07943 published May 14,1992 and in Richard C. Mulligan, “Gene Transfer and GeneTherapy:Principle, Prospects and Perspective” in Enology of HumanDisease at the DNA Level, Chapter 12. J. Linsten and A. Peterson, eds.Rover Press, 1991 which are both incorporated herein by reference.

By using developing dendritic cells to charge MHC class I and/or IIproducts, several desirable components of T cell modulation in situ canbe achieved. Antigen uptake and presentation by immature progenitors,allows the APC to tailor the peptides that are appropriate for anindividual's MHC products, and increases the number of specializedstimulatory APCs. These properties of dendritic cell progenitorpopulations meet many of the demands for using cells as vehicles foractive immunization and immunotherapy in situ.

The present invention provides for the first time a method of obtainingdendritic cells in sufficient quantities to be used to treat or immunizeanimals or humans with dendritic cells which have been activated withantigens. In addition, dendritic cells may be obtained in sufficientquantities to be useful as reagents to modify antigens in a manner tomake the antigens more effective as T-cell dependent antigens.

To use antigen-activated dendritic cells as a therapeutic or immunogenthe antigen-activated dendritic cells are injected by any method whichelicits an immune response into a syngeneic animal or human. Preferably,dendritic cells are injected back into the same animal or human fromwhom the source tissue was obtained. The injection site may besubcutaneous, intraperitoneal, intramuscular, intradermal, orintravenous. The number of antigen-activated dendritic cells reinjectedback into the animal or human in need of treatment may vary depending oninter alia, the antigen and size of the individual. A key feature in thefunction of dendritic cells in situ is the capacity to migrate or hometo the T-dependent regions of lymphoid tissues, where the dendriticcells would be in an optimal position to select the requisiteantigen-reactive T cells from the pool of recirculating quiescentlymphocytes and thereby initiate the T-dependent response.

According to the preferred method of stimulating an immune response inan individual, a tissue source from that individual would be identifiedto provide the dendritic cell precursors. If blood is used as the tissuesource preferably the individual is first treated with cytokine tostimulate hematopoieses. After isolation and expansion of the dendriticcell precursor population, the cells are contacted with the antigen.Preferably, contact with the antigen is conducted in vitro. Aftersufficient time has elapsed to allow the cells to process and presentthe antigen on their surfaces, the cell-antigen complexes are put backinto the individual in sufficient quantity to evoke an immune response.Preferably between 1×10⁶ and 10×10⁶ antigen presenting cells areinjected back into the individual.

The novel antigens of the invention are prepared by combining substancesto be modified or other antigens with the dendritic cells preparedaccording to the method of the invention. The dendritic cells process ormodify antigens in a manner which promotes the stimulation of T-cells bythe processed or modified antigens. Such dendritic cell modifiedantigens are advantageous because they can be more specific and havefewer undesirable epitopes than non-modified T-dependent antigens. Thedendritic cell modified antigens may be purified by standard biochemicalmethods. For example, it is known to use antibodies to products of themajor histocompatibility complex (MHC) to select MHC-antigenic peptidecomplexes and then to elute the requisite processed peptides with acid[Rudensky et al., Nature 353:622-7 (1991); Hunt et al., Science 255:1261-3 (1992) which are incorporated herein by reference].

Antigen-activated dendritic cells and dendritic cell modified antigensmay both be used to elicit an immune response against an antigen. Theactivated dendritic cells or modified antigens may by used as vaccinesto prevent future infection or may be used to activate the immune systemto treat ongoing disease. The activated dendritic cells or modifiedantigens may be formulated for use as vaccines or pharmaceuticalcompositions with suitable carriers such as physiological saline orother injectable liquids. The vaccines or pharmaceutical compositionscomprising the modified antigens or the antigen-activated dendriticcells of the invention would be administered in therapeuticallyeffective amounts sufficient to elicit an immune response. Preferably,between about 1 to 100 micrograms of modified antigen, or its equivalentwhen bound to dendritic cells, should be administered per dose.

The present invention also provides a method and composition fortreating autoimmune disease. Such autoimmune diseases include but arenot limited to juvenile diabetes, multiple sclerosis, myasthenia gravisand atopic dermatitis. Without being bound by theory, it is believedthat autoimmune diseases result from an immune response being directedagainst “self-proteins”, i.e., autoantigens that are present orendogenous in an individual. In an autoimmune response, these“self-proteins” are being presented to T cells which cause the T cellsto become “self-reactive”. According to the method of the invention,dendritic cells are pulsed with the endogenous antigen to produce therelevant “self-peptide”. The relevant self-peptide is different for eachindividual because MHC products are highly polymorphic and eachindividual MHC molecules might bind different peptide fragments. The“self-peptide” may then be used to design competing peptides or toinduce tolerance to the self protein in the individual in need oftreatment.

Because dendritic cells can now be grown from precursors according tothe methods and principles identified here, and because dendritic cellscan modify antigens to produce killer T cells, the compositions of thisinvention are particularly useful as vaccines towards viruses and tumorcells for which killer T cells might provide resistance.

EXAMPLES Example 1 Production of Mouse Dendritic Cells In Vitro fromProliferating Dendritic Cell Precursors from Blood Materials

A. Mice: BALB/C, BALB/C×DBA/2 F1, BALB/C×C57BL/6 F1, C57BL/6×DBA/2 F1,and C57BL/6 males and females, 6-8 weeks of age were purchased fromJapan SLC Inc [Shizuoka, Japan], the Trudeau Institute [Saranac Lake,N.Y.], and Charles River Wiga [Sulzberg, FRG]. Four preparations ofrGM-CSF were evaluated with similar results, the yield of dendriticcells reaching a plateau with 30-100 U/ml. The preparations were fromDr. S. Gillis, Immunex Corp, Seattle Wash.; Genetics Institute[supernatant from COS cells transfected with mGM-CSF; used at 30 U/ml orgreater]; and Dr. T. Sudo [supernatant from CHO cells transfected withthe expression vector, pHSmGM-CSF (22), and E. Coli expressed material].B. Blood Preparation: Blood was obtained by cardiac puncture or from thecarotid artery. The blood was diluted in, or allowed to drip into,RPMI-1640 with 100 U/ml heparin [about 2 ml/mouse]. Blood cells werepelleted at 1000 rpm at 4°, resuspended in RPMI 1640, and sedimentedagain. The pellet was suspended in 1 ml RPMI 1640 per mouse and mixedwith an equal volume of 1.66% ammonium chloride in distilled water tolyse the red cells. After 2 min at room temperature, the suspension wasspun at 1000 rpm at 4°. The pellet, which still contained red cells, wasresuspended again in 0.5 ml RPMI and 0.5 ml NH₄Cl for 2 min, diluted inRPMI, and sedimented again. After 2 more washes, most platelets and redcells had been depleted and a population of blood leukocytes had beenobtained.C. Aggregates of Proliferating Dendritic Cells from Blood Supplementedwith GM-CSF

Blood leukocytes, usually from C×D2 F1 mice, were cultured in 16 mmtissue culture wells [24 well dishes, Costar, #25820] in medium (1 mlper well) supplemented with GM-CSF at 30 U/ml and at 1.5×10⁶ cells/well.The medium was RPMI 1640 supplemented with 5% fetal calf serum (JRHBiosciences, Lenexa, Kans.), 50 uM 2-ME, 20 ug/ml gentamicin, andrecombinant mouse GM-CSF. After overnight culture, many monocytesadhered and the nonadherent cells were transferred to new 16 mm wells.The adherent cells did not develop dendritic cell colonies, but duringthe next week, the nonadherent populations exhibited three changes.First, most of the lymphocytes and granulocytes died or could be removedby washing. Second, the surface of the well became covered with amonolayer of tightly adherent cells that included macrophages andfibroblasts. Third, affixed to scattered sites on the monolayer, theredeveloped small aggregates of cells. The cultures were fed with GM-CSF(30 u/ml) at day 6-7 and then every 3 days by aspirating 0.5-0.75 ml ofthe medium and adding back an equal volume of fresh medium with GM-CSF.The aggregates continued to expand in number and size. At about day 10,the cells were ready to be subcultured. Any residual loose cells couldbe rinsed off prior to dislodging the aggregates into fresh medium andGM-CSF. About 0.8-1 million dislodged cells per original well weredivided into 3 subculture wells.

Most of the aggregates disassembled during this first subculture, whilethe bulk of the adherent monolayer remained attached to the originalwell. Upon transfer, most of the cells in the dislodged aggregatesadhered as single cells to the new culture well but over a period of 2-3days, aggregates reappeared. The aggregates again were affixed toadherent stromal cells, but these adherent cells were much less numerousthan the dense monolayer in the original culture. Over the next 4-7days, aggregates filled the wells. These colonies were often larger thanthose of the original wells and were covered with many sheet-likeprocesses typical of dendritic cells. It was more difficult to countcells at this point, since many of the aggregates contained a core oftightly associated cells. However, the number of single cells that couldbe recovered per well expanded about 2 fold between days 10 and 17 ofculture.

If the cultures were allowed to overgrow, some cells with the morphologyof dendritic cells were released. More typically, the cells were notallowed to overgrow and the aggregates were dislodged and subculturedagain at about 20 days. Prior to subculture, the aggregates could bepurified from free cells by 1 g sedimentation. Such separations weremore easily performed with longer periods of culture, i.e., it waseasier to isolate intact aggregates at 3 vs. 2 vs. 1 week of culture.With additional subculturing, the number of aggregates that wereproduced per well was progressively reduced. However colonies of growingcells, as confirmed by 3H-TdR labeling and autoradiography [below],could be generated in subcultures for 1-2 months. Following subculturingat 2-3 weeks, typical single dendritic cells were now released into themedium. By direct observation with video recording, these released cellshad the active motility of dendritic cells, continually extending andretracting large veils or sheet-like processes. In the presence ofcontinued GM-CSF, one observed both free dendritic cells as well asexpanding colonies. In the absence of GM-CSF, only free dendritic cellswere released and the aggregates essentially fell apart and did notreform in the medium and colonies of aggregates did not develop. Theyields of free dendritic cells per subculture ranged from 0.3-2.5×10⁵.

In summary, from a starting blood mononuclear culture of 1.5×10⁶ cells,where dendritic cells were difficult to detect, we on average obtained5-10 subcultures each with at least 3-10×10⁴ released dendritic cells at3 weeks, as well as many aggregates capable of further proliferation.Therefore aggregates of growing cells were developing in mouse bloodsupplemented with GM-CSF, and these aggregates were covered withdendritic cells many of which could be released spontaneously into themedium.

D. Phenotype of the Cell Aggregates and Dendritic Cells ReleasedTherefrom

Cytospin preparations were made in a Shandon cytocentrifuge using3-10×10⁴ cells. The slides were stored with desiccant prior to fixationin acetone and staining with mAb followed by peroxidase mouse anti-ratIg [Boehringer Mannheim Biochemicals, #605-545] or rabbit anti-hamsterIg [Accurate Chemical & Scientific Corp, #JZY-036-003]. The preparationswere stained with Giemsa and mounted in Permount for bright fieldanalysis. For cytofluorography [FACScan, Becton Dickinson], aliquots ofcells were stained with primary rat or hamster mAb followed by FITCmouse anti-rat Ig [Boehringer, #605-540] or biotin rabbit anti-hamsterIg [Accurate, JZY-066-003] and FITC-avidin.

Cytospin preparations of 2-3 week cultures were examined with a panel ofmAb and an immunoperoxidase method. The released cells, and many of thecells that could be dislodged from the periphery of the aggregate, weresimilar in their stellate shape and phenotype. Most of the cells stainedstrongly with mAb to MHC class II, the CD45 leukocyte common antigen,CR3 receptor CD11b, and heat stable antigen (HSA), and CD44. Stainingwith mAbs to the Fc receptor [2.4G2] and macrophage F4/80 antigen (MAC)was weak or undetectable in >95% of the cells. The cultures containedonly rare B cells [B220 mAb, RA-3], T cells [thy-1 mAb, B5-5], orgranulocytes [GRAN, mAb RB6]. Some cells at the periphery of theaggregate, and many of the cells that were released from the aggregates,were stained with two markers that are largely restricted to dendriticcells. The interdigitating cell antigen [mAb NLDC 145 (13), IDC], whichalso binds to thymic epithelium, stained many but not all of thedendritic profiles. Virtually all of the dendritic profiles stained withmAbs 2A1 and M342 stain granules in the perinuclear region of maturedendritic cells, B lymphocytes, as well as interdigitating cells insections through the T areas of lymphoid organs. Macrophages from manysites [blood monocytes; peritoneal cavity macrophages; macrophages insections of lymph node, thymus, spleen] do not contain 2A1 orM342-reactive granules.

Cytofluorography was used to gain semi-quantitative information on theexpression of antigens at the cell surface. A panel of mAb were appliedto two populations: cells that could be dislodged from the aggregates byPasteur pipetting, and cells that were released spontaneously when theaggregates were subcultured for 1 day. These “dislodged” and “released”populations were identical in their dendritic shape and in phenotype butfor some exceptions that are considered below. The phenotype of thereleased cells is shown in FIG. 2, and the few differences betweenaggregated and released cells are in FIG. 3. Virtually all the dendriticcells developing in and from the aggregates expressed high levels of theleukocyte common [CD45, mAb M1/9.3] and heat stable [mAbs M1/69 andJ11d] antigens, as well as high levels of CD44 and CD11b [mAb M1/70].Low levels of the following antigens were detected on the cell surface:the dendritic cell antigen 33D1, the macrophage marker F4/80, the Fcγreceptor antigen 2.4G2, the p55 IL-2 receptor CD25 antigen 3C7, and theCD11c integrin N418 [FIG. 2]. These antigens were noted on all cells byFACS even though many of the antigens like F4/80 and 2.4G2 were weak orabsent in the cytoplasm with an immunoperoxidase method. Severalantigens were absent: RB6 granulocyte, RA3 B cell, B5-5 thy-1, GK 1.5CD4, and SER-4 marginal zone macrophage [FIG. 2].

Expression of class I and II MHC products by the dendritic cells inthese cultures was very high but nonetheless bimodal [FIG. 2 and FIG.3]. Most of the dendritic cells that were dislodged from the aggregateshad somewhat lower levels of MHC class I and II, while dendritic cellsthat were released from the aggregates had very high levels of MHCproducts. The other marker that was different in the released andloosely attached dendritic cells was NLDC 145 which was higher in thereleased population. [FIG. 3, top panels]. We conclude that thephenotype of the cells that arise from the proliferating aggregates isvery much like that seen in cultured dendritic cells from skin, spleen,and thymus (24, 28) with the exception that the M1/70 CD11b marker ismore abundant.

E. 3H-TdR Autoradiography to Verify Growth of Dendritic Cell Precursors

After 2 and 3 weeks in liquid culture, the wells contained numerousexpanding aggregates of cells, and in some cases were already releasingnonadherent dendritic cells in large numbers. Cultures were labeled with3H-thymidine to identify and phenotype the proliferating cells and theirprogeny. For pulse labeling, 3H-TdR was added to the cultures [6 Ci/mM,1 uCi/ml final]. 2 h later, the medium was replaced with 3H-TdR freemedium, and the cultures were separated into nonadherent released cellsand residual adherent aggregates for examination on cytospinpreparations [Shandon Inc, Pittsburgh Pa., #59900102]. The cytospincells were stained for specific antigens with mAb and immunoperoxidaseas above. Also, the slides were dipped in photographic emulsion [Kodakautoradiography emulsion type NTB2 #165-4433] for exposure [5 days]prior to development, staining with Giemsa, and mounting in Permount.For pulse chase experiments, a lower dose of 3H-TdR was used to maintaincell viability, but the cells were handled similarly otherwise. Thepulse was applied at 0.1 uCi/ml for 2 h or for 16 h, the latter toprovide higher initial labeling indices. The cells were washed andchased for 1-3 days prior to harvesting and analysis as above withimmunoperoxidase, autoradiography, and Giemsa staining.

The 2 and 3 week cultures were exposed to 3H-TdR and examined forproliferative activity. The labeled cells were washed, spun onto slides,and the cytospins stained with mAb and an immunoperoxidase method priorto dipping and exposure to photographic emulsion. Important markers weremAbs 2A1 and NLDC-145 which recognize intracellular granules and a cellsurface antigen in mature dendritic cells respectively.

When cultures were labeled with a 2 h pulse of 3H-TdR, it was apparentthat the labeling index in the aggregates was very high, at least 10-15%of the profiles in the aggregates being in S phase. In contrast, if3H-TdR was applied to cultures that were releasing typical nonadherentdendritic cells, the released fraction contained only rare labeledprofiles. If GM-CSF was removed, 3H-TdR labeling ceased within a day.Virtually all the 3H-TdR labeled cells in the aggregate failed to labelwith mAb to markers found on mature dendritic cells i.e., 2A1 andNLDC145. The level of staining with anti-MHC class II mAb was less onthe cells in S-phase than in the released dendritic cell populations[not shown].

Pulse chase experiments were then done to establish that labeled cellsin the aggregate were giving rise to typical dendritic cells. Cultureswere first exposed to a low dose of 3H-TdR, either for 2 h or for 16 h,the latter to label a larger percentage of the cells in the aggregates.The wells were washed free of radiolabel, and then the aggregates weredislodged and separated from free cells by 1 g sedimentation. Theaggregates were transferred to fresh medium without radiolabel, and overthe next 1-3 days of culture, many dendritic cells were released intothe medium. When the “chased” cultures were examined, several findingswere apparent. The labeling index remained high, i.e., most of theprogeny of cells that were proliferating in the aggregates were notbeing lost from the cultures. Second, the grain counts were dilutedseveral fold from those apparent in the original pulse. Third, cellsexpressing the markers of mature dendritic cells [NLDC145, the 2A1granular antigen, high levels of MHC class II] were now radiolabeled.Therefore the cellular aggregates that GM-CSF was inducing in culturedmouse blood were actively proliferating and releasing nonproliferatingprogeny with many of the typical cytologic and antigenic features ofmature dendritic cells including the 2A1 granular antigen, the NLDC145marker, and high levels of MHC class II.

F. Accessory Cell Function for T Cell Proliferative Responses

MLR stimulating activity was monitored in the GM-CSF treated bloodcultures. Cells from the blood cultures were exposed to 1500 rads[137Cs] and applied in graded doses to 3×10⁵ purified syngeneic orallogeneic T cells in 96 well, flat-bottomed microtest wells. The Tcells were nylon wool nonadherent, spleen and lymph node suspensionsthat were treated with anti-Ia plus J11d mAbs and complement to removeresidual APC. 3H-TdR uptake was measured at 72-86 h [6 Ci/mM, 4 uCi/mlfinal].

Initially there was little or no MLR stimulating activity [FIG. 4, ★].Some stimulating activity was noted at day 1 of culture [FIG. 4, ◯]. Anexamination of cytospin preparations revealed that these 1 daynonadherent blood cells had a low [<0.3%] but clear subset of Ia-rich,dendritic profiles. By day 7, when the proliferating aggregates werefirst evident on the monolayer, the stimulating activity of thedislodged aggregates had increased further, but was still 100 times lessin specific activity than typical dendritic cells (FIG. 4, compare Δ and) even though most of the cells at day 7 and subsequent time pointswere MHC class II positive. By day 14, at which time typical nonadherentdendritic cells were just beginning to be released from the aggregates,the nonadherent population had considerable MLR stimulating activity,[FIG. 4, ∇]. After 3 weeks, typical mature dendritic cells had becomeabundant, and these indeed stimulated comparably to their spleniccounterparts [FIG. 4, compare ⋄ and ]. Other cells in the culture, suchas those dislodged from the aggregates, were about 10 fold less activethan dendritic cells [FIG. 4, ♦]. We conclude that the aggregates ofproliferating dendritic cells have some MLR stimulating activity butthat it is the mature released cells that are fully potent, some 100-300times more active on a per cell basis than the populations in thestarting culture at 1-7 days. During day 7-20 of culture, total cellnumbers also expanded at least 5-10 fold.

G. Homing Activity of Dendritic Cells in Vivo

A second specialized feature of dendritic cells is their capacity tohome to the T areas of peripheral lymphoid tissues (8, 10). Dendriticcells or other cell types were labeled at 2-10×10⁶/ml withcarboxyfluorescein for 10 min on ice [Molecular Probes C-1157; 30 uMfinal concentration in Hanks balanced salt solution (HBSS) with 5% FCS],washed in RPMI 1640, and injected in a volume of 50 ul RPMI-1640 intothe foot pads. One day later, the draining popliteal lymph nodes wereremoved, frozen in OCT medium, and sectioned [10μ] in a cryostat. Tosample the entire node, we took duplicate specimens at regularintervals. The sections were applied to multiwell slides [CarlsonScientific microslides #111006], stored at −20° C., dried in adesiccator 30′ prior to use [or left at room temp overnight], fixed inacetone, and stained with a peroxidase conjugated rabbit anti-FITCantibody [Dakopatts, P404]. To verify that the dendritic cells in thelymph node were in the T-dependent areas as described (8), we addedappropriate mAb to B cell, T cells, macrophages, or dendritic cells andvisualized the latter with alkaline phosphatase conjugated mouseanti-rat Ig [Boehringer Mannheim, #605-5357] plus a chromogen kit[Biomeda Corp, Foster City Calif. #S04]. We then blocked endogenousperoxidase with “Endo Blocker” [Biomeda Corp, #M69] followed by theperoxidase anti-FITC as above.

Blood leukocytes, even when given at a dose of 10⁶ cells per footpad,failed to home to the lymphoid organ. When we tested dendritic cellsthat had been generated with GM-CSF from blood, homing to the T area wasobserved with injections of 200,000 cells. The selective localization tothe T areas was confirmed by double labeling the specimens with mAb thatstain B cells or T cells. Therefore dendritic cells produced in culturehave the key functional features of this lineage: homing to theT-dependent regions and strong accessory activity.

H. Requirements for Generating Dendritic Cell Colonies from Blood

The surface phenotype of the blood cell that gives rise to the dendriticcell colonies was assessed by treating the starting population withantibodies and complement. Treatment with either 33D1 anti-dendriticcell, anti-MHC class II, or anti thy-1 did not eliminate the colonyforming unit [not shown]. Instead, removal of thy-1⁺ or Ia⁺ cellsenriched colony numbers several fold. CSF's other than GM-CSF were alsotested, either at the start of the 1-3 week culture, or upon transfer of2-3 week old aggregates to form veiled cells. None of the CSF's tested,i.e., IL-3, M-CSF, G-CSF, SCF, supported the formation of colonies ormature dendritic cells. Therefore the growing dendritic colonies arevery much dependent upon GM-CSF.

In an effort to identify proliferating precursors to the dendritic cellsystem, we set up cultures from several tissues that lacked maturedendritic cells and supplemented these with different growth factorsparticularly the CSF's [M-CSF, G-CSF, IL-3, GM-CSF, IL-1, and SCF].Dendritic cell precursors were not observed from neonatal epidermis,which contains mainly Ia⁻ Langerhans cells (29). To avoid overgrowth ofgranulocytes in bulk bone marrow cultures which may make theidentification of typical cell colonies or large numbers of dendriticcells difficult, it is preferred to remove the nonadherent,proliferating granulocytes on days 2 and 4. Blood, which has few typicaldendritic cells in the mouse (30), proved to be very effective forobtaining dendritic cell precursors. Growing cell aggregates appearedafter about 6 days in culture, and these were often covered withprofiles having the unusual and motile processes of dendritic cells.With time, typical nonadherent dendritic cells were released. The latterhad the morphology and movement of dendritic cells as previouslydescribed in cultured mouse spleen, mouse skin, lymph from severalspecies, and human blood (25-27). Therefore to identify proliferatingdendritic bells, it seems critical to begin with an appropriate startingpopulation, preferably blood, and to supplement the culture with GM-CSF.

Without wishing to be bound by any theory, we think that the initialaggregates that appeared in the cultures represented clones, since verysmall groups of 4-6 cells were observed early on e.g., day 5. We triedto prove that the aggregates were clonal by mixing blood cells fromstrains that were distinguished with markers to polymorphic antigenslike CD44 and MHC class II. However we could not complete theexperiments since we found that mouse strains differed in the number andspeed with which colonies developed. BALB/C and DBA [and F1 strainsderived therefrom] were the most active; B6 and B10 were several timesless active; and strains like CBA/J, C3H/He, and A/J were poor sourcesof proliferating, dendritic cell aggregates.

The precursors to the aggregates of proliferating dendritic cells werenot typical monocytes or dendritic cells, because the number ofaggregates that developed could be increased substantially if onedepleted monocytes by adherence or Ia-positive cells with antibody andcomplement. Without wishing to be bound by theory, we tentativelyconclude that blood contains an Ia-negative precursor that forms aproliferating aggregate. In the aggregate, dendritic cells mature andare released as nonproliferating progeny.

The formation of aggregates of dendritic cells required exogenousGM-CSF. If the aggregates were placed in macrophage orgranulocyte-restricted CSF's [M-CSF, G-CSF], proliferation ceased andneither macrophages nor granulocytes were formed. Because the culturescontained macrophages and some stromal cells, in addition to thedendritic cell aggregates, it was possible that other cytokines werebeing produced that were critical to the formation of dendritic cells.It appears however that the cells in the aggregates have lostresponsiveness to M- and G-CSF, and that dendritic cells represent adistinct myeloid pathway of development. Perhaps, without wishing to bebound by theory, the pathway originates from a common precursor in whichthe dendritic cell lineage is an offshoot that no longer responds tomacrophage and granulocyte restricted CSF's.

Labeling with 3H-thymidine, using pulse and pulse-chase protocols, wasimportant in establishing the precursor-product relationships that weretaking place in these liquid cultures. In a 2 h pulse, virtually everylabeled cell lacked two typical markers of mature dendritic cells, i.e.,the NLDC-145 interdigitating cell surface antigen (13) and the recentlyidentified 2A1/M342 granular cytoplasmic antigens (34). These mAb do notstain most macrophage populations that we have examined either asisolated cells [blood, spleen, peritoneal macrophages] or in sections[thymic cortex, spleen red pulp, lymph node medulla]. In pulse chaseprotocols, large numbers of labeled progeny were released from theaggregates, and these released cells were nonadherent, motile, andstrongly stimulatory in the MLR. After combined autoradiography andimmunoperoxidase labeling, the labeled progeny carried the granularantigens, the NLDC-145 antigen, and very high levels of MHC class II.Each of these cytologic and antigenic markers are largely restricted todendritic cells.

Without wishing to be bound by theory, we believe that maturation totypical nonproliferating dendritic cells occurred within the aggregate.The aggregates were covered with cells with the sheetlike or veiledprocesses of dendritic cells. Cells with markers of mature dendriticcell markers [high MHC class II, 2A1 positive granules, NLDC antigen]were also observed at the periphery of the cell aggregates. However, itwas difficult to isolate the aggregate intact, i.e., without dislodgingthese more mature cells. The mechanism whereby dendritic cells maturedand left the aggregate was not clear. Maturation was enhanced in oldercultures [>2 weeks] or by removing adherent stroma cells. Bothproliferation and maturation was blocked if the cultures contained toomany fibroblasts.

The functional maturation that occurred in the proliferating aggregateis striking. The dendritic cells that were generated in culture werepotent MLR stimulators. 100 dendritic cells induced a much strongerprimary MLR than 100,000 blood leukocytes. The increase in stimulatingactivity per Ia-positive cell was at least 2 logs between the time thatthe aggregates first appeared and the time that typical dendritic cellswere released in large numbers. Over this time period, cell recoveryincreased 5-10 fold. Also the dendritic cell progeny homed in a preciseway to the T cell area of lymph node, another functional property thatwas not detectable in blood cells [data not shown].

Example 2 Generation of Large Numbers of Dendritic Cells from Mouse BoneMarrow Cultures Supplemented with GM-CSF MATERIALS

A. Mice: Female BALB/C, male DBA/2, and female C57BL/6 mice, 7 wks old,were purchased from Japan SLC [Hamamatsu, Shizuoka, Japan]. BALB/C×DBA/2F1, of both sexes 7-10 wks old, were from Japan SLC and the TrudeauInstitute, Saranac Lake, N.Y.Reagents: The culture medium was RPMI-1640 [Nissui, Tokyo, Japan; GIBCO,Grand Island, N.Y.] supplemented with 5% FCS, 50 μM 2-Mercaptoethanol,and 20 μg/ml gentamicin. Murine rGM-CSF [10⁸ U/mg protein] was kindlyprovided by Kirin Brewery Co [Maebashi, Gumma, Japan]. A panel of ratand hamster mAbs to mouse leukocyte antigens is described elsewhere (23,24). FITC- and peroxidase-conjugated mouse anti-rat IgG were purchasedfrom Boehringer Mannheim [Indianapolis, Ind.] and FITC- andperoxidase-conjugated goat anti-hamster Ig [γ and L-chain] were fromJackson Immunoresearch Lab [Westgrove, Pa.] and Caltag [San Francisco,Calif.] respectively.B. Bone marrow cultures: After removing all muscle tissues with gauzefrom the mouse femurs and tibias, the bones were placed in a 60 mm dishwith 7011 alcohol for 1 min, washed twice with PBS, and transferred intoa fresh dish with RPMI-1640. Both ends of the bones were cut withscissors in the dish, and then the marrow was flushed out using 2 ml ofRPMI-1640 with a syringe and 25G needle. The tissue was suspended,passed through nylon mesh to remove small pieces of bone and debris, andred cells were lysed with ammonium chloride. After washing, lymphocytesand Ia-positive cells were killed with a cocktail of mAbs and rabbitcomplement for 60 min at 37° C. The mAbs were GK 1.5 anti-CD4, HO 2.2anti-CD8, B21-2 anti-Ia, and RA3-3A1/6.1 anti-B220/CD45R all obtainedfrom the ATCC [TIB 207, 150, 229, and 146 respectively]. 7.5-10×10⁵cells were placed in 24 well plates [Nunc, Naperville, Ill.] in 1 ml ofmedium supplemented with 500-1000 U/ml rGM-CSF. The cultures wereusually fed every 2 d for about 2 to 10 days, by gently swirling theplates, aspirating ¾ of the medium, and adding back fresh medium withGM-CSF. An object of these washes was to remove nonadherent granulocyteswithout dislodging clusters of developing dendritic cells that wereloosely attached to firmly adherent macrophages.

To enrich for growing dendritic cells, we utilized a procedure similarto that described for the mouse blood cell cultures of Example 1.Briefly, the aggregates of attached cells were dislodged with Pasteurpipettes and applied to 6 ml columns of 50% FCS-RPMI 1640. Residualgranulocytes in the cultures, often in aggregates as well, were easilydissociated at this step. Upon 1 g sedimentation of the dislodged cells,clusters moved to the bottom of the tube and single granulocytes wereleft at the top. The aggregates were subcultured at 2-3×10⁵/ml in freshmedium with GM-CSF, typically for 1 day in 16 mm wells. After overnightculture, large numbers of typical dendritic cells were released.Adherent macrophages also expanded in these cultures, but most remainedfirmly adherent to the culture surface.

C. Cytological Comparison of Dendritic Cell Precursors and Ia-Negative,Bone Marrow Nonlymphocytes

To compare the released [dendritic-cell enriched; top] and adherent[macrophage-enriched; bottom] fractions of 7 day bone marrow cultures,Ia-negative, bone marrow nonlymphocytes were cultured in GM-CSF. At days2 and 4, nonadherent cells were gently washed away and at day 6, theloosely attached cell aggregates were isolated by 1 g sedimentation.After a day in culture, the cells that were released from the aggregateswere cytospun onto glass slides and stained with different mAbs plusperoxidase anti-Ig as well as Giemsa and nonspecific esterase. Thefirmly adherent cells in the original cultures were dislodged with EDTAand also cytospun. Many dendritic profiles are in the released fraction[a hand lens is useful to detect cell shape and contaminatinggranulocytes, in the Giemsa stain], while the adherent cells are for themost part typical vacuolated macrophages. Strong MHC class II expressionoccurs on all released cells but for a few typical granulocytes. Only asubset of the firmly adherent cells express class II. Most releasedcells express the 2A1 endocytic vacuole antigen, while the adherentcells are 2A1 weak or negative.

D. Cell surface and intracellular antigens: Cell surface stainingutilized cytofluorography [FACScan; Becton Dickinson, Mountain ViewCalif.]. Staining with primary rat or hamster mAbs was followed byFITC-conjugated mouse anti-rat or goat anti-hamster Ig's as described inExample 1D. A panel of mAbs to cell surface (23, 24) and tointracellular antigens (33, 34) was tested on cytospin preparations. Westudied both adherent and nonadherent populations, the former beingdislodged in the presence of 10 mM EDTA [the adherent cells were rinsedtwice with PBS and once with EDTA-PBS, and then incubated with EDTA-PBSfor 20 min at 37° C.]. The cytospins were fixed in acetone and stainedwith mAbs followed by peroxidase conjugated anti-rat or anti-hamster Ig.The peroxidase was visualized with diaminobenzidine, and the nucleicounterstained with Giemsa.E. Cytologic assays: Giemsa stains were performed on cytospinpreparations as was the case for the nonspecific esterase [α-naphthylacetate as substrate] stain using standard methods (35) except that thecytospin preps were fixed with 2% glutaraldehyde in Hanks medium insteadof buffered acetone formalin. Phase contrast observations, usually ofliving cells, were made with inverted microscopes [Nikon Diaphot] at afinal magnification of 100 and 400×. Transmission electron microscopy(36) and ³H-thymidine autoradiography were performed on developingdendritic cells as described in Example 1E.F. Mixed leukocyte reactions: Cells from the bone marrow cultures wereexposed to 15 Gy of X-ray irradiation and applied in graded doses to3×10⁵ syngeneic or allogeneic T cells in 96 well flat bottomed cultureplates for 4d. The T cells were prepared by passing spleen and lymphnode suspensions through nylon wool and then depleting residual APCswith anti-Ia plus J11d mAbs plus complement. 3H-thymidine uptake wasmeasured at 80-94 h after a pulse of 4 uCi/ml [222 GBq/mmol; AmericanRadiolabeled Chemicals, Inc, St. Louis, Mo.].G. Aggregates of Proliferating Dendritic Cells from Mouse Bone MarrowSupplemented with GM-CSF.

Prior to culture, we treated the marrow suspensions with a cocktail ofmAbs to B cells, T cells, and MHC class II antigens plus complement.This pretreatment of bone marrow cells which reduces the number of Bcells and granulocytes, is necessary to identify growing dendritic cellsin bone marrow because B cells and granulocyte are also GM-CSFresponsive and proliferate and mask the presence of dendritic cellprecursors.

Accordingly, at d2 and d4 of culture, we gently swirled the plates toremove loosely adherent cells which proved to be granulocytes typical inmorphology and expression of the RB6 antigen [see below]. With thesesteps, we recognized by day 4 cellular aggregates attached to a layer ofadherent cells. Some of the profiles in the aggregates had the veil orsheet-like processes of dendritic cells. The aggregates could bedislodged by gentle pipetting and separated by 1 g sedimentation. Within3 h of replating, many spiny adherent cells emigrated from the clustersand had the appearance of fresh splenic adherent cells (13). Afteranother day of culture, these adherent cells came off the surface andmany typical dendritic cells were seen floating in the culture medium.Optimal yields of dendritic cells were obtained when the aggregates wereharvested on day 6 and then cultured overnight. The capacity of bonemarrow to generate dendritic cells is striking, >5×10⁶ from the 4 majorhind limb bones in a week.

Attached to the surface of the culture wells were cells with thecytologic features of macrophages, and these also expanded in numbersduring the first week of culture. These cells could be dislodged bypipetting after incubation at 37° C. in the presence of 10 mM EDTA.

If the cultures were maintained in M-CSF, large numbers of macrophagesgrew out and were firmly attached to the plastic surface. However, nodendritic cells or dendritic cell aggregates were apparent. If a mixtureof M-CSF and GM-CSF was applied, then colonies of adherent macrophagesas well as aggregates of growing granulocytes and dendritic cells werenoted.

H. Development of Potent MLR Stimulator Cells in Bone Marrow Cultures

It is known that suspensions of mouse bone marrow are not active as MLRstimulators (38) and do not contain detectable dendritic cells (30).Given the cytologic observations above, we cultured Ia-negative, bonemarrow nonlymphocytes for 6d and checked MLR stimulating activity atdaily intervals. As long as the cultures were supplemented with GM-CSF,strong MLR stimulating activity developed [FIG. 5]. The increase wasprogressive and by day 6, as few as 100 of the marrow cells induced MLRswith stimulation indices of 20 or more.

To correlate the development of MLR stimulating activity with theappearance of dendritic cells in these heterogenous cultures, we firstseparated the cultures into nonadherent and loosely adherent fractions[FIG. 6A]. The nonadherent cells, which were mainly granulocytes in thefirst 4 days, were obtained by gently swirling the plates and harvestingthe cells. The loosely adherent cells, which contained the aggregates ofpresumptive dendritic cell precursors and dendritic cells at day 4 andlater times, were dislodged by pipetting over the surface of firmlyadherent stromal cells. At d2 and at d4, the most potent stimulatingactivity was in the adherent fraction. By d6, the nonadherent fractionwas very active. If one tested firmly adherent macrophages, there was noMLR stimulating activity [FIG. 6B, open squares].

As mentioned above, in the presence of GM-CSF the cultures developedaggregates of growing cells that release typical dendritic cells betweend4-8 of culture. These aggregates could be isolated by gentle pipettingover the monolayer followed by 1 g sedimentation. When the aggregateswere returned to culture, populations enriched in dendritic cells werereleased, and these released cells proved to have the very strong MLRstimulating activity that is characteristic of dendritic cells [FIG.6B].

I. Cell Surface Markers—Cytofluorography

By cytofluorography, two populations of cells were readily distinguishedin the nonadherent or easily dislodged cells. One population had a lowforward light scatter, high levels of the RB6 antigen, and low levels ofMHC class II. The other population was larger and had the reciprocalphenotype. The aggregated cells were enriched relative to unfractionatedcultures in MHC class II positive cells [FIG. 8, compare left andmiddle], and the level of MHC class II on individual cells increasedwhen the aggregates were cultured overnight to release highly enrichedpopulations of dendritic cells [FIG. 8, compare middle and right]. MoreMHC class II rich, RB6 antigen negative cells were seen in day 6 versesday 4 cultures [FIG. 8]. None of the cells reacted with the mAbs to theB220 antigen of B cells or the SER-4 antigen of macrophages [not shown].

More detailed FACS studies were performed on cells that had beenreleased from the aggregates. The granulocytes were gated out on thebasis of lower forward light scattering. The larger, dendritic cells haduniformly high levels of MHC class I and II as well as CD44 and CD11b[Mac-1; M1/70]. Intermediate level staining was noted for the heatstable antigen [HSA; M1/69], CD45 [M1/9.3], and CD18 [2E6]. Lower levelstaining was evident for the low affinity IL-2 receptor [CD25, 7D4],interdigitating cell antigen [NLDC-145], Fcγ receptor [2.4G2], dendriticcell antigen [33D1], macrophage antigen [F4/80], and CD11c p150/90β2-integrin [N418]. Several antigens were not detectable includingphagocyte [SER-4 marginal zone macrophage, RB6 granulocyte] andlymphocyte [RA3-6.1 B lymphocyte; thy-1, CD3, 4, 8 T lymphocyte]markers. This phenotype is similar in many respects to that seen insplenic and epidermal dendritic cells (24, 27, 28). The one exception isthe high level in the marrow-derived cells of CD11b, an integrin thathelps mediate emigration of myeloid cells from the vasculature.

J. Cytospin Preparations

Cytospins were prepared to further compare the released dendritic cellswith the firmly adherent stromal population. By Giemsa stain, the cellsthat had released from the aggregates had the typical stellate shape ofdendritic cells, while the adherent cells were for the most partvacuolated macrophages. Many of the dendritic cells had a perinuclearspot of nonspecific esterase stain, while the more adherent populationshad abundant cytoplasmic esterase.

The released cells stained strongly for MHC class II products, exceptfor the contaminants with typical granulocyte nuclei. The stronglyadherent cells contained a subpopulation of class II positive cells.Recently antigens have been described that are primarily localized inintracellular vacuoles of dendritic cells and B cells but notmononuclear phagocytes. The antibodies are termed M342 (34) and 2A1.Many of the dendritic cells had strong 2A1 stain, and a smaller numberexpressed M342. The adherent cells had a few profiles with weak 2A1.

The development of Ia-positive cells, and cells expressing granularintracellular antigens, was quantitated on cytospins. [FIG. 10]. MHCclass II antigens were expressed first, followed by the 2A1 and M342granular antigens. [FIG. 10]. By day 8, the majority of the cells weredendritic and had high levels of MHC class II products and 2A1 antigen.If granulocytes were not removed from the cultures, the yield ofnonadherent cells was much larger but the highest percentage of MHCclass II positive cells that we detected was 30%, and it was difficultto identify and isolate the aggregates that were the site of dendriticcell growth.

When the cytospins were stained for other myeloid antigens, the releasedcells stained weakly and sometimes not at all above background withmonoclonals to the Fcγ receptor [2.4G2] and macrophage restrictedantigen [F4/80]. Most of the firmly adherent cells in contrast stainedstrongly for both antigens. This suggests that while low levels of 2.4G2and F4/80 are found on the surface of the released dendritic cells,synthesis and expression are probably being downregulated much as occurswhen epidermal dendritic cells are placed in culture (27).

On day 4, some 30-50,000 Ia-positive cells were floating in thecultures, while on both day 6 and on day 8, another 50-100,000Ia-positive cells were harvested. The quantitative data indicated thateach well produced some 200,000 or more Ia-positive cells in a week.Since we obtain about 20-30 wells of the starting Ia-negative marrowcells from two tibia and two femurs, the total yield of Ia-positivecells is 5×10⁶ or more, exceeding the total estimated number ofLangerhans cells in the skin of a mouse (27).

K. 3H-Thymidine Pulse Chase Experiments

To further document the proliferation and differentiation of dendriticcells in these cultures, clusters of cells were isolated on day 4,exposed to a 12 h pulse of ³H-thymidine, and examined by autoradiographyimmediately or after 1, 2 and 3 days of chase in ³H-thymidine freemedium. The majority of cells in the aggregate were labeled initially,and almost all cells released from the aggregates were labeled. Duringthe chase, increasing percentages of the released progeny expressed the2A1 granule antigen of mature dendritic cells.

L. Electron Microscopy

The released cells had many large veils or lamellipodia extending fromseveral directions of the cell body. The cytoplasm had manymitochondria, few electron dense granules and lysosomes, but severalelectron lucent vesicles some with the cytologic features ofmultivesicular bodies. The numerous cell processes extending from thedendritic cells were evident in the semi-thin sections of ourpreparations.

A bone marrow-derived dendritic cell at d5 of culture shows manycytoplasmic veils. A close up of the perinuclear region shows profilesof smooth reticulum and vacuoles. There are few lysosomal or phagocyticstructures.

Example 3 Mouse Dendritic Cell Progenitors Phagocytose ParticulatesSensitizing Mice to Mycobacterial Antigens In Vivo Material and Methods

A. Mice: BALB/C×DBA/2 F1, C57BL/6×DBA/2 F1, and BALB/C male and femalemice were purchased from the Trudeau Institute [Saranac Lake, N.Y.] andJapan SLC [Hamamatsu] and used at 6-10 weeks of age.B. Bone marrow cultures: As described in Example 2 above, bone marrowwas flushed from the femus and tibias, depleted of red cells with 0.83%ammonium chloride, and cultured in 24 well plates [Nunc, Napaville, Ill.and Corning #25820, Corning N.Y.] at 10⁶ cells/well in 1 ml of RPMI-1640supplemented with 5% fetal calf serum, 20 ug/ml gentamicin, and 1000U/ml of recombinant murine GM-CSF [Kiren Brewery, Maebashi, Gumma,Japan; 9.7×10⁷ U/mg]. At d2, 0.75 ml of medium and the nonadherent cellswere removed, and replaced with fresh medium. This was repeated at d4-5,thereby removing most of the developing granulocytes and leaving behindclusters of proliferating dendritic cells adherent to a stroma thatincluded scattered macrophages. The culture medium was then supplementedwith particulates of BCG mycobacteria [described in greater detailbelow], and phagocytosis was allowed to proceed for 20-24 h usually ond5-6. At this point the cultures were rinsed free of loose cells andparticles, and the cells analyzed immediately for particle uptake.Alternatively cells in the washed cultures were dislodged and 3-4×10⁶cells transferred to a 60 mm Petri dish for a 1 or 2 day “chase” periodin particle-free, fresh, GM-CSF supplemented medium. Class II-rich,mature dendritic cells developed during the chase as described inExample 2, and these were isolated by cell sorting [below]. To comparethe phagocytic activity of developing and mature dendritic cells,particles were also administered to 7-8d bone marrow cultures that arerich in single nonproliferating mature dendritic cells.C. Particulates: BCG mycobacteria [Trudeau Institute, 1.5-2.5×10⁸CFU/ml; Kyowa Pharmaceutical Industries, Tokyo] were administered atapproximately 10⁷ live BCG per 16 mm diameter well. Uptake was assessedfollowing an “acid fast” stain using an auramine-rhodamine procedurethat is more sensitive than Ziehl Neelsen and facilitates organismcounts. Colloidal carbon [Pellikan Ink, Hannover, Germany] was added at1:2000 dilution. The carbon was identified as a black granular stain inspecimens stained with Diff-Quik^(R) [Baxter Healthcare Corp, Miami,Fla.]. Suspensions of 2u latex particles [0.5% v/v; Seradyn,Indianapolis, Ind.] were applied to the cultures at 50 ul/well, a dosewhich covers the surface of the culture well with beads.

D. Isolation of Mature Dendritic Cells by Cell Sorting:

As noted before in Example 2, the dendritic cells that are produced inGM-CSF stimulated bone marrow cultures express very high levels ofsurface MHC class II products [monoclonals B21-2, TIB 227 and M5/114,TIB 120 from the ATCC] as well as moderate levels of a dendriticcell-restricted antigen recognized by monoclonal NLDC-145. Immediatelyafter the pulse with BCG, or after an additional 2 days of “chase”culture, the cells were stained with biotin B21-2 and FITC-streptavidin[Tago, Burlingame, Calif.]. Class II-rich cells then were sorted[FACStar Plus, Becton Dickinson, Mountainview, Calif.] and cytospun ontoglass slides [Shandon Inst. Sewicky, Pa.]. The sorted cells were stainedwith Diff Quick® which outlines the stellate shape of dendritic cells incytospins and allows enumeration of profiles containing perinucleardepots of internalized colloidal carbon or latex spheres. To visualizeBCG, the cytospins were fixed in absolute acetone for 10 min at roomtemperature and stained with M5/114 anti-class II, NLDC-145anti-dendritic cell, or RA3-6B2 anti-B220 or anti-B cell [the latter asa control] followed by POX conjugated mouse anti-rat Ig [BoehringerMannheim, Indianapolis, Ind.] and diaminobenzidine tetraHCl [PolyscienceInc, Warrington, Pa.]. The preparations were then double labeled foracid-fast bacilli with auramine rhodamine. Virtually all the cells inthe preparation were rich in NLDC-145 and MHC class II products. Thenumber of BCG bacilli in at least 400 cells were enumerated.

E. Electron microscopy: To prove that cell-associated BCG were allinternalized, the dendritic cells produced in pulse chase protocols[above] were fixed in 2.5% glutaraldehyde and processed for EM asdescribed in Example 2.F. Antigen presentation in vitro: Mice were primed with completeFreunds' adjuvant [CFA, SIGMA, St. Louis, Mo.; 25 ul in the fore andrear paws] or as a control, mycobacteria-free incomplete Freunds'[ICFA]. 7-14d later, the draining lymph nodes were dissociated into asingle cell suspension and depleted of APCs with mAbs to MHC class 11,B220, and heat stable antigens [M5/114 anti-Ia, RA3-6B2 anti-B220, andJ11d anti-HSA; TIB 120, 146, and 183 from the ATCC respectively] andrabbit complement. 3×10⁵ of these APC-depleted; primed T cells werecultured in 96 well flat-bottomed microtest wells [Corning #25860] inRPMI-1640 medium supplemented with 0.5 k mouse serum and 50 uM2-mercaptoethanol. Graded doses of BCG-pulsed, bone marrow or spleenAPCs were added. 1 uCi of 3H-thymidine [NEN, Boston, Mass.; 20 Ci/mmol;4 uCi/ml] uptake was added to monitor DNA synthesis at 72-88 h. Datashown are means of triplicates in which standard errors were <15% of themean.G. Antigen presentation in vivo: APCs that had been pulsed with antigenin vitro were administered in vivo to unprimed C×D2 F1 mice. To prime Tcells in draining lymph node, 2×10⁵ dendritic cells were injected intothe paws, and lymph node cells were prepared 5d later. To prime T cellsin spleen, 10⁶ cells were injected i.v., and splenocytes were prepared 5or 10d later. To measure T cell priming, bulk lymph node or spleen cellswere cultured as above and challenged with graded doses of proteinantigens, either purified protein derivative [PPD, from StatenserumInstitute, Copenhagen, Denmark, or from Dr. Ichiro Toida, ResearchInstitute for BCG in Japan, Kiyose, Tokyo] or bovine serum albumin[Sigma] and 3H-thymidine measured at 72-88 h. To characterize theproliferating cells, the populations were treated with antibodies andcomplement prior to measuring 3H-thymidine uptake.H. Phagocytosis of Latex Particles within Clusters of DevelopingDendritic Cells: Pulse and Pulse Chase Protocols

When mouse bone marrow or blood is stimulated with GM-CSF, proliferatingcell aggregates appear, and these give rise to large numbers of typicalimmunostimulatory dendritic cells. In bone marrow, which was used forthe experiments described below, the proliferating aggregates are bestidentified by washing away the majority of nonadherent granulocytes thatare also induced by GM-CSF in the cultures. At d5-6, the time point whenthe aggregates were first sizable [5-10 cells wide], we applieddifferent particles over a 20-22 h period.

Following administration of 2u latex spheres, heavy labeling was notedin scattered macrophages on the monolayer. In addition, some clearlabeling occurred within the developing dendritic cell aggregates [FIG.12A]. Aggregates that had been exposed to particles were recultured anadditional 2 days. During this time, large numbers of cells werereleased into suspension. These primarily were mature dendritic cellswith characteristic stellate shapes and high levels of MHC class II andNLDC-145 antigens. When the released cells were examined by lightmicroscopy, many contained latex spheres and often around a clearperinuclear zone or centrosphere [FIG. 12B]. We also studied colloidalcarbon uptake in a similar manner. When aggregates were pulsed withcolloid and mature dendritic cells allowed to form during a chaseperiod, some of the released cells had a centrosphere with small butclear cut carbon deposits [FIG. 12C]. In contrast, when latex or carbonwas offered to mature dendritic cells, little uptake occurred [FIG.12D].

I. BCG Mycobacteria Uptake by Developing Dendritic Cells—Acid FastStains

Live BCG mycobacteria were administered as the phagocytic meal over a20-22 h period using the protocol for administering latex particlesdescribed above. Cell-associated bacilli were visualized by a sensitivefluorescent acid-fast stain. Following the 20 h pulse, the developingdendritic cell aggregates contained many organisms. To isolate the moremature dendritic cells from the cultures, the cells were resuspended andsorted those cells with high levels of MHC class II products.Immediately after the BCG pulse, about 20% of the sorted cells containedacid fast bacilli [Table 1]. The majority of MHC class II-weak cellswere not studied further because of excessive stickiness during cellsorting.

Companion cell cultures were then studied after 2 days of a chaseculture. Because many mature dendritic cells formed during the chaseperiod, the number of Ia-rich progeny had increased four fold [Table 1].

TABLE 1 Frequency of dendritic cells with phagocytosed BCG organisms inGM-CSF stimulated mouse bone marrow cultures Exp't BCG # cells % #BCG/ #exposure counted phagocytic DC 1 d5-6 pulse 469 18.1 2.6 498 18.5 2.5 2d5-6 pulse 444 22.5 3.0 463 22.2 2.9 pulse, 2d chase 564 57.1 3.8 57957.0 3.2 3 d5-6 pulse 440 21.8 2.1 623 22.8 2.9 pulse, 2d chase 187 50.32.9 511 58.7 4.

Quantitative data of dendritic cells containing BCG. Mouse bone marrowcultures were stimulated in 16 mm wells for 5d with GM-CSF, washed, andexposed to BCG organisms for 20 h. The cultures were washed again andeither examined immediately, or pooled and transferred to a 60 mm dishfor an additional 2d chase culture. The dendritic cells in the cultureswere selected as Ia-rich cells using a fluorescent activated cell sorterand then cytospun onto glass slides for staining for acid fast bacilli.During the chase period, the percentage of Ia-rich cells in the culturesincreased 2-2.5 fold, and the total number of cells increased 2 fold,resulting in a 4-5 fold increase in the number of Ia-rich cells.

The percentage of dendritic cells containing BCG also rose to 50% [Table1, FIG. 13]. Double labeling experiments verified that cells with acidfast bacilli expressed MHC class II and the dendritic cell-restrictedNLDC 145 antigen FIG. 13. Because the total number of MHC class II andNLDC-145 positive cells had increased 4-fold in just 2d, it is likelythat these BCG-laden dendritic cells were derived from less mature butphagocytic progenitors in the aggregates.

J. Electron Microscopy of BCG Pulsed APCs

The perinuclear location of the cell-associated particles by lightmicroscopy indicated that organisms had been internalized. The matterwas verified by electron microscopy. About 50% of the dendritic cellprofiles contained internalized BCG, although the number of organismsper profile was small, usually one but only up to four, FIGS. 14 A, B.Each organism seemed to occupy its own vacuole. It appeared that aphagosomal membrane closely approximated most bacilli, FIG. 14 C, D.

K. Presentation In Vitro of Mycobacterial Antigens to Primed T Cells

To test the presenting function of dendritic cells that had been pulsedor pulse-chased with BCG organisms, we first prepared antigen-responsiveT cells from the draining lymph nodes of mice that had been injectedwith CFA [complete Freund's adjuvant, which contains heat-killedmycobacteria] or with incomplete Freund's adjuvant [IFA as control; seeMethods]. When dendritic cells were added to IFA-primed T cells, asyngeneic mixed leukocyte reaction was observed. This was comparablewhether or not the APCs had been exposed to BCG. [FIG. 15, right].However, when dendritic cells had been pulsed with BCG and added toCFA-primed T cells, strong proliferative responses were induced [FIG.15, left]. If dendritic cells were tested immediately after the one daypulse, or after an additional 2 day chase period, the chased populationwas much more potent. [FIG. 15, left; compare ♦ and ▾]. As few as 100BCG pulse-chased, dendritic cells elicited sizable T cell responses invitro [FIG. 15, left ♦]. The BCG pulse-chased populations also were 5-10times more potent in inducing responsiveness to mycobacterial antigenthan mature dendritic cells freshly exposed to either PPD or BCG. [FIG.15 left, compare ♦ with , ▴]. Therefore, it appeared that the extent ofphagocytosis correlated with the efficacy of presentation, as the pulsechased populations were the most active APCs and contained the mostintracellular BCG. [Table 1].

L. Presentation In Vivo of Mycobacterial Antigens to Unsensitized Mice

Comparable populations of BCG-pulsed, and BCG-pulsed and chased, APCswere tested for the capacity to present mycobacterial antigens tounprimed mice. Following injection into the footpads, strongresponsiveness to PPD was observed. [FIG. 16]. Again the dendritic cellswere the most potent if tested after a 2d chase [FIG. 16; compare ⋄ andΔ], and this chase period greatly increased the total yield of dendriticcells.

To test if the increased antigen presenting function of BCG pulse-chaseddendritic cells was related to the increased number of APCs carryingBCG, the primed populations were also tested for responsiveness tobovine serum albumin [BSA], since the dendritic cells had been grown inthe presence of fetal calf serum. All the dendritic cell populations,regardless of the details of the exposure to BCG, primed mice similarlyto BSA. [FIG. 16, filled symbols]. This indicates that each populationwas comparably efficient in immunizing to a soluble protein, whereas thedendritic cells that had phagocytosed BCG were more effective ineliciting responses to mycobacterial antigens.

The surface markers of the primed cells were tested by antibody andcomplement mediated lysis of the populations prior to measuring3H-thymidine uptake [data not shown]. The proliferating cells werepositive for thy-1, but negative for MHC class II, heat stable antigen,and B220. Anti-CD4 hybridoma culture supernatant blocked proliferationmore than 85% i.e., the primed cells were helper-type T cells.

Priming was also observed when spleen T cells were tested after anintravenous infusion of BCG-pulsed and BCG-pulse chased dendritic cells[FIG. 17]. The cells were more responsive at 5 versus 10 days afterinjection [compare FIGS. 17 A and C]. Again dendritic cells that hadbeen cultured [“chased”] for 2 days after exposure to BCG were the mostpotent [FIG. 12 compare ♦ with ▴; but all populations primed the spleencells similarly to BSA [FIG. 17B]. We conclude that dendritic cellprogenitors capture and retain mycobacterial antigens in a manner thatis highly immunogenic in vivo.

Example 4 Antigen Activated Dendritic Cells as Immunogens

Dendritic cells prepared according to the method described in Example 1are plated at a concentration of approximately 1×10⁵ cells per well of a24 well plastic culture plate. The cells are incubated in RPMI 1640containing 5% fetal calf serum and GM-CSF (30 u/ml). Antigen is added tothe dendritic cell cultures and the cultures are incubated with antigenfor approximately 4 hours or for sufficient time to allow the dendriticcells to handle the antigen in an immunologically relevant form, or in aform that can be recognized by T cells. Such handling of the antigen bythe dendritic cells involves the dendritic cells 1) acquiring, 2)processing, and 3) presenting the antigen to the T cells in a form whichis recognized by the T cells. Following binding of the antigen to thedendritic cells the cells are collected from the culture and used toimmunize syngeneic mice. The activated dendritic cells are injectedsubcutaneously into the mice in an amount sufficient to induce an immuneresponse to the antigen.

Example 5 Dendritic Cell Modified Antigen

Dendritic cells prepared as described in Example 1 are pulsed with aprotein antigen for a time sufficient to allow the dendritic cells toacquire, process and present the modified antigen on the surface of thedendritic cells. The dendritic cells are then collected from the culturefor extraction of the modified antigen.

For extraction of the modified antigen, the dendritic cells aresolubilized with detergent to extract the modified antigen bound to MHCmolecules. The MHC molecules bound to modified antigen are purified byprecipitation with antibodies which bind the MHC molecules such as MH2.The modified antigens are extracted from the precipitate for analysis.

Example 6 Preparation of Dendritic Cells from Human Blood A. Patients

Seventeen experiments were performed with blood from human patientsundergoing consolidation chemotherapy (15 with leukemias/lymphomas infull remission, 2 with solid tumors) followed by treatment with G-CSF.Three experiments were performed with blood from patients afterchemotherapy (1 (acute myeloic) leukemia, 2 solid tumors) and GM-CSFtreatment. The results of three experiments, two from the G-CSF treatedgroup of patients, A and B, and one from the GM-CSF treated group ofpatients, C, are presented.

B. Rationale

Results of procedures described in Example 1 relating to mouse blood andExample 2 relating to bone marrow (J. Exp. Med. 175:1157-1167, 1992 andJ. Exp. Med. 176:1693-1702, 1992), identified several features ofdendritic cell growth and development: (a) dendritic cell progenitors donot express the MHC class II antigens that are typical of matureimmunostimulatory progeny and of many other cell types (B cells,monocytes); (b) dendritic cell progenitors require GM-CSF and perhapsother cytokines that can be provided by the cells in culture or assupplements to proliferate and mature; (c) critical steps in dendriticcell growth and development take place in distinctive aggregates thatare loosely adherent to standard tissue culture surfaces; (d) bymonitoring the appearance of these aggregates, one can evaluate thenumerous variables that are pertinent to the generation of dendriticcells, a trace but specialized type of antigen presenting cell thatoperates in a potent fashion to induce T cell immunity and tolerance insitu (Ann. Rev. Immunol. 9:271-1296, 1991).

C. Protocol

1. Blood mononuclear cells were isolated by sedimentation in standarddense media, here Lymphoprep (Nycomed, Oslo).

2. The isolated mononuclear cells were depleted of cells that were notdendritic cell progenitors. These contaminants were coated withmonoclonal antibodies to CD3 and HLA-DR antigens and depleted on petridishes coated with affinity-purified, goat anti-mouse IgG (“panning”).

3. 10⁶ cells in 1 ml of culture medium were plated in 16 mm diameterplastic culture wells (Costar, Rochester, N.Y.). The medium wasRPMI-1640 supplemented with 50 uM 2-mercaptoethanol, 10 mM glutamine, 50ug/ml gentamicin, 5% serum from cord blood (without heat inactivation)or 5% fetal calf serum (with inactivation), and 400 U/ml humanrecombinant GM-CSF. Every 2nd day thereafter and for a total of 16 days,the cultures were fed by removing 0.3 ml of the medium and replacingthis with 0.5 ml of fresh medium supplemented with the cytokines.

Cells were cultured under the following conditions: 1) without presenceof additional cytokines; 2) GM-CSF, 400 or 800 U/ml; 3) GM-CSF, 400 or800 U/ml, plus IL-1α, 50 LAF units/ml for the last 24 h of culture; 4)GM-CSF, 400 or 800 U/ml, plus TNFα, 50 U/ml; 5) GM-CSF, 400 or 800 U/ml,plus TNF-α, 50 U/ml, plus IL-11α, 50 LAF units/ml for the last 24 h ofculture; 6) GM-CSF, 400 or 800 U/ml, plus IL-3, 100 U/ml; 7) GM-CSF, 400or 800 U/ml, plus IL-3, 100 U/ml, plus IL-1α, 50 LAF units/ml for thelast 24 h.

In experiment C, non-dendritic cells which sank in dense metrizamidewere also tested.

4. Characteristic proliferating dendritic cell aggregates (hereaftertermed “balls”) appeared by the 5th day, as evident upon examinationwith an inverted phase contrast microscope. These balls expanded in sizeover the course of a week (day 5-11). Some balls appeared in theoriginal wells (steps 3 and 4), but typically these did not enlarge tothe same extent as the nonadherent wells (step 4). The wells must besubcultured, e.g., 1 well split into 2-3 wells, as cell densityincreases.

5. Two alternative approaches were used to isolate the mature dendriticcells from the growing cultures. One method consisted of removing cellsthat were nonadherent and separate the balls from nonballs by 1 gsedimentation. Dendritic cells were then released in large numbers fromthe balls over an additional 1-2 days of culture, and mature dendriticcells were isolated from the nonballs by floatation on dense metrizamideas described (Freudenthal and Steinman, Proc. Natl. Acad. Sci. USA87:7698-7702, 1990). The second method is simpler but essentiallyterminates the growth phase of the procedure. According to the secondprocedure, the nonadherent cells were harvested when the balls were verylarge. The cells were left on ice for 20 minutes, resuspended vigorouslywith a pipette to disaggregate the balls, and the mature dendritic cellswere floated on metrizamide columns.

6. To demonstrate the immunostimulatory activity of the dendritic cellprogeny, graded doses of irradiated cells (30 to 30,000 in serial 3 folddilutions) were added to accessory cell-depleted T cells (200,000 forthe mixed leukocyte reaction assay, MLR; 150,000 for the oxidativemitogenesis assay, OXMI). The T cell response was measured with a 16 hpulse of 3H-thymidine on the 5th (MLR) or 2nd day (OXMI). Tcell-stimulation experiments (oxidative mitogenesis and mixed leukocytereaction) were performed in the presence of 1 microgram/ml indomethacin.Data from three MLR experiments are presented in FIGS. 18A, B, and C.

D. Results

1. GM-CSF is an essential cytokine. G-CSF, M-CSF, IL-3, or no cytokinedo not permit the development of dendritic cell balls. GM-CSF at 400-800U/ml is optimal, irregardless of whether donors had been treated witheither. GM-CSF or G-CSF to expand the number of myeloid progenitor cellsin blood. Addition of TNFα at 10-50 U/ml usually but not alwaysincreased dendritic cell yields up to two-fold (cf. Caux et al., (1990)Tumor necrosis factor alpha strongly potentiates interleukin-3 andgranulocyte-macrophage colony-stimulating factor-induced proliferationof human hematopoietic CD34+ progenitor cells, Blood 2292-2298). Asevident from the representative experiments described in FIGS. 18A, Band C, TNFα supplementation also substantially improves the function ofthe dendritic cell progeny. rhu IL-1α (50 LAF units/ml) in someexperiments proves a further increase in function, when added during thelast 24 h of the culture. Experiments with tissue from patients withsolid tumors or leukemias/lymphomas gave comparable results with regardto the generation of dendritic cells.

2. Starting from 60 ml of blood, and after culturing in the presence ofGM-CSF only, the yield of typical mature immunostimulatory dendriticcells was 6−12×10⁶ cells, representing 40-80% of the total cells. Thisyield is at least 20 times greater than the yield of mature dendriticcells in 60 ml of fresh blood which would be at most 5% (3-6×10⁵) ofthis (Proc. Natl. Acad. Sci. 87:7698-7702, 1990).

3. The phenotype of the dendritic cells generated by this methodincluded the fact that the cells were strongly positive for HLA-DR, MHCclass II products but negative for CD1a, CD14, and B cell markers.

4. The development of granulocytes in the cultures reduces the purity ofthe dendritic cells. Typically, these granulocyte balls are moreadherent and are left behind at the day 2 transfer step of the protocol.If these adherent granulocyte colonies reappear, simply transfer thegrowing dendritic cells may be transferred to another well.

Example 7

Other sources of dendritic cell progenitors have been tested accordingto the method described in Example 6:

a) For two patients, a small sample of bone marrow was also provided.When the above procedure was applied, the dendritic cell balls andmature immunostimulatory dendritic cells were formed in large numbers.

b) Blood from 7 normal donors has been evaluated using the methoddescribed in Example 6. The number of balls proved to be much less(10-20/well of 2×10⁶ cells), but the use of normal blood is obviouslysimpler and has the advantage that granulocyte colonies do not form asnoted before (comment 5) in comparing mouse blood and marrow, J. Exp.Med. 175:1157-1167, 1992 vs. J. Exp. Med. 176:1693-1702, 1992).

c) Fetal or umbilical cord blood was also tested, because it toocontains more progenitor cells than adult blood. Since the number ofCD34+ progenitors is still very small (about 1%), we tested the simplermethod above in which CD34+ cells are not purified initially. DC ballsare readily induced, except that red blood cells which are toxic weredepleted. By adding the anti-erythroid monoclonal VIE-G4 (provided byDr. W. Knapp, Vienna) to the panning step (step 2), and using anadditional floatation on Lymphoprep (step 1) after panning. The yieldsof dendritic cells from cord blood are roughly comparable to thatdescribed in the method (1-5×10⁶ dendritic cells, representing 20-40% ofthe total cells from 40 ml cord blood without a metrizamide floatationstep). The balls are more adherent, and the dendritic cells expressCD1a, in contrast to adult blood.

Example 8 Generation of Large Numbers of Dendritic Cells from HumanBlood Cultures Supplemented with GM-CSF and IL-4 Materials

A. Culture medium: was RPMI 1640 supplemented with 200 mM L-glutamine,50 mM 2-ME, 20 mg/ml gentamicin, and either 5-10% FCS [56° C., 0.5 h;Seromed, Biochrom KG, Berlin, Germany), or, in some experiments with 5%cord blood serum.B. Recombinant human cytokines: GM-CSF (3.1×10⁶ U/mg) was kindlyprovided by Dr. E. Liehl (Sandoz Research Institute, Vienna, Austria),TNFa (6×10⁷ U/mg) by Dr. G. R. Adolf (Ernst Boehringer Institut fürArzneimittelforschung, Vienna, Austria), and IL-1a [3×10⁸ U (D10assay)/mg] by Dr. P. Lomedico (Hoffmann La Roche Inc., Nutley, N.J.,USA). IL-4 was commercially obtained material (1×10⁷ U/mg) (Genzyme Co.,Boston, Mass.) or supernatant from IL-4 gene transfected COS cells(3×10⁴ U/ml) kindly provided by Dr. G. Le Gros (Ciba-Geigy Ltd., Basel,Switzerland). M-CSF (1.9×10⁶ U/mg) was a gift of Dr. S. Clark, GeneticsInstitute, Cambridge, Mass. IL-3 and G-CSF were purchased from GenzymeCo.C. Monoclonal Antibodies: We used the following mouse mAb's (referencedin Lenz, et al., (1993) J. Clin. Invest. 92:2587 unless defined here):W6/32, anti-HLA-A,B,C (HB95 from the ATCC); L243, anti-HLA-DR(Becton-Dickinson [BD], Mountain View, Calif.); 9.3F10, anti-HLA-DR+DQ(HB180 from ATCC); RFD1, anti-HLA-DQ-related (gift of L. W. Poulter,London, England); B7/21, anti-HLA-DP (BD); UCHL-1, anti-CD45RO (DakoCorp., Glostrup, Denmark); 4G10, anti-CD45RA; 3C10 and LeuM3 (BD),anti-CD14; EBM11, anti-CD68 (Dako); LeuM1, anti-CD15 (BD); LeuM9,anti-CD33 (BD); HPCA-1, anti-CD34 (BD); Leu11b, anti-CD16 (BD); 2A3,anti-CD25 (BD); IV.3 (C. L. Anderson, Columbus, Ohio) and CIKM5 (G.Pilkington, Melbourne, Australia), ant—FcgRII/CD32; 15-1, anti-FceRI(J.-P. Kinet, Rockville, Md., Wang, et al, (1992) J. Exp. Med.,175:1353; OKT-6, anti-CD1a (Ortho Pharmaceuticals, Raritan, N.J.); Leu4(BD) and OKT-3 (Ortho), anti-CD3; Leu3a+b, anti-CD4 (BD); Leu1, anti-CD5(BD); Leu2a, anti-CD8 (BD); Leu12, anti-CD19 (BD); Leu16, anti-CD20(BD); VIB-E3, anti-CD24 (W. Knapp, Vienna, Austria); G28-5, anti-CD40(J. A. Ledbetter, Seattle, Wash.); TB133, anti-LFA-1/CD11a and CLB54,anti-CD18 (both from S. T. Pals, Amsterdam, The Netherlands); LeuM5,anti-CD11c (BD); 7F7, anti-ICAM-1/CD54 (M. P. Dierich, Innsbruck,Austria); AICD58, anti-LFA-3/CD58 (Immunotech, Marseille, France); BB1,anti-B7/BB1/CD80 (E. A. Clark, Seattle, Wash.); Lag,anti-Birbeck-granule-associated (M. Kashihara-Sawami, Kyoto, JapanKashihara, et al., (1986) J. Invest. Dermatol., 87:602); VIE-G4,anti-glycophorin (O. Majdic, Vienna, Austria); Ki-67,proliferation-associated antigen (Dako, Gerdes, et al., (1984) J.Immunol., 133:1710).D. Culture of DC from cord blood: Cord blood was collected according toinstitutional guidelines during normal full-term deliveries. PBMC(peripheral blood mononuclear cells) were isolated by flotation onLymphoprep (Nycomed, Oslo, Norway), washed, incubated once in saturatingconcentrations of anti-glycophorin mAb, anti HLA-DR and anti CD3,washed, panned (10 min. on ice, then 20 min. at RT) twice onto bacterialpetridishes coated with goat anti-mouse Ig (H+L) Ab (Jackson Lab.,Avondale, Pa.). The nonadherent fractions were then plated in 24-welldishes (Costar, Cambridge, Mass., USA) and cultured as described indetail in Results.E. Culture of DC from blood of cancer patients: Peripheral blood wasobtained with informed consent from cancer patients in completeremission during hematopoietic recovery following high-doseconsolidation chemotherapy and administration of G-CSF [300 μg humanrG-CSF (Neupogen, Hoffmann-La-Roche Ltd.) s.c./d] (15 patients withleukemias/lymphomas, 2 with solid tumors) or GM-CSF [400 μg (Leukomax,Sandoz Ges m.b.H) s.c./d] (1 patient with leukemia, 2 with solidtumors]. PBMC were prepared by sedimentation in Lymphoprep, coated withanti HLA-DR+anti CD3 mAb's, washed, and panned twice as described above.Non-adherent, depleted fractions were then processed according to theprotocol described in detail in Results.F. Culture of DC from blood of heal thy adults: PBMC were obtained fromeither 40 to 100 ml heparinized fresh whole blood or leukocyte-enrichedbuffy coats (Freudenthal, P. S. and R. M. Steinman (1990) Proc. Natl.Acad. Sci. USA 87:698, and processed as described in detail in Results.G. Phenotypic analysis: Phenotypic analysis was performed exactly asdescribed previously in Romani, et al., (1989) J. Invest. Dermatol.,93:600 by immunolabeling and flow cytometry analysis, and byimmunoperoxidase/-fluorescence on cells cytospun or attached bypoly-L-lysine to glass slides.H. T cell stimulation assays: Allogeneic 1° MLR (mixed luihexytereaction) and oxidative mitogenesis were performed exactly as describedin Romani, et al., (1989) J. Invest. Dermatol., 93:600.I. Cord blood mononuclear cells as a source for DC progenitors: Threedifferent situations to generate DCs from proliferating progenitors orprecursors in blood were evaluated. Our goals were to define requisitecriteria and cytokines for proliferating DCs, but at the same time toavoid the need to enrich for CD34+ progenitor populations which are sofew in number. We began with cord blood, since a prior report had shownthat 0.5-1×10⁶ enriched [>95%] CD34+ cord blood cells could give rise to1-2.5×10⁷ DCS if cultured for 14 days in a combination of GM-CSF and TNF(Caux, et al., (1992) Nature, 360:258). A limitation to this previousprotocol was that cord blood only contains 0.9-2.6% CD34+ cells (Mayani,et al., (1993) Blood, 81:3252). Therefore we modified the techniquedescribed above used with adult mouse blood (Example 1), in whichun-fractionated cells, or MHC class II negative cells, were cultured inGM-CSF. We found that the varying, yet substantial percentage ofnucleated erythroid cells in human cord blood was toxic and that thesecould be removed by panning with anti-glycophorin A mAb. We began, thenwith erythroid-depleted cord blood cells with a low buoyant density[<1.077 g/ml] and plated these at 1-2×10⁶/ml in 1 ml of standard mediumsupplemented with GM-CSF [400-800 U/ml]+/−TNF [50 U/ml]. The wells werefed every other day by aspirating 0.3 ml medium and adding back 0.5 mlmedium with cytokines.

The subsequent events were similar to those described previously withmouse blood. First, small adherent aggregates appeared after 4-7d [FIG.19A and FIG. 19B]. Many of the peripheral cells displayed a veiled ordendritic appearance, and these adhered loosely to a nest ofspindle-shaped cells. Nonadherent cells could be removed by carefullyrinsing in warm medium, but this was not essential. The adherentaggregates enlarged over the next 7-10d, indicating proliferativeactivity [FIG. 19C]. Then typical “veiled” DCs [FIG. 19D-FIG. 19E] werereleased. These DC aggregates only developed if GM-CSF was added to themedium. TNF-α although not essential, increased aggregate size and DCyield 50-100%. It was advantageous to remove the TNF-α during the last1-2d of culture to permit the release of single, mature DCs.

The released DCs were identified by three sets of criteria. First, thecells by inverted phase contrast microscopy showed characteristic thinmotile cytoplasmic processes or veils [FIG. 19D-FIG. 19E]. By EM, thetypical ultrastructure of DCs was noted [see below, FIG. 24]. Only oneLangerhans cell granule (=Birbeck granule) was found in 100 cellprofiles. Second, the DCs had the standard phenotype i.e., HLA-DR richbut negative for markers of other cells e.g., CD3/14/19/20. Likeepidermal Langerhans cells, CD1a was detected but only 1-2% of the cellsreacted with an antigen associated with Langerhans cell granules[anti-Lag] (Kashihara, et al., (1986) J. Invest. Dermatol., 87:602), andthese interestingly were in the center of rare residual aggregates.Third, the cord blood derived DCs were potent stimulators of resting Tcells in the primary MLR [FIG. 20A] as well as oxidative mitogenesis[not shown]. The inclusion of TNF in the culture medium increased theimmunostimulatory function of the DCs [FIG. 20A].

The above protocol has proven reproducible in 21 standardizedexperiments and generates 1-5×10⁶ DCs from 40 ml of cord blood at apurity of 20-50% (Table II). Purity can be increased to >80% byflotation on metrizamide (Freudenthal, P. S. and R. M. Steinman, (1990)Proc. Natl. Acad. Sci. USA, 87:7698) columns. We conclude (a) it is notnecessary to enrich for CD34+ precursors to generate typical DCs fromcord blood, and (b) the criteria that proved useful in identifyingaggregates of proliferating progenitors in mouse blood are alsoapplicable to human cells.

J. DC progenitors in the blood of cancer patients during hematopoieticrecovery from chemotherapy: We next studied blood mononuclear cells fromcancer patients in full remission [leukemias/lymphomas and solid tumors]following high-dose chemotherapy and either G-CSF [17 patients] orGM-CSF [3 patients] treatment. It is known that in the hematopoieticrecovery of such patients, progenitors are mobilized into the blood insubstantial numbers [0.5-6.0% CD34+ cells] (Eaves, C. J. (1993) Blood,82:1957; Pettengell, et al., (1993) Blood, 82:3770). Instead ofenriching for CD34+ cells, we simply removed CD3+ and DR+ cells bypanning, and then plated 1-2×10⁶ cells in 1 ml medium with 5-10% FCS or5% cord serum plus 400-800 U/ml GM-CSF. The nonadherent cells weretransferred at d2 (or in some experiments at d1) and cultured for 16dfeeding every other day.

Growing DC aggregates appeared on day 3-5 and expanded in size until day11 [not shown, but compare FIG. 21]. The aggregates developed peripheralveils, and initially were loosely attached to a stroma but later werenonadherent. The wells were subcultured e.g., 1 well split to 2-3 wells,when the cell density increased or if more tightly adherent, smooth,non-DC clusters appeared [contaminating macrophage and granulocyteprogenitors]. When the DC aggregates became very large (d12-d16), it waseasy to dissociate the cells and float the mature DCs on metrizamidecolumns.

The DCs that developed in this manner had a typical morphology by lightand electron microscopy [not shown, but see FIGS. 21 and 24]. Thephenotype was again MHC class II rich but null for CD3/14/19/20 [notshown]. MLR stimulatory function was potent [FIG. 20B]. In contrast tocord blood derived DCs, CD1a and Lag antigens were not seen (not shown).

GM-CSF proved essential for DC development. G-CSF, M-CSF and IL-3 wereinactive. Exposure to 3000 rads of ionizing irradiation blocked DCdevelopment. Addition of TNF-α at 10-50 U/ml usually though not alwaysincreased DC yields up to 2 fold, and always improved the function ofDCs [FIG. 20B]. Human rIL-1 [50 LAF unit/ml], when added during the last24 h in some experiments, further increased function [FIG. 20B].

Starting from 40 ml blood, and using both GM-CSF and TNF-α, the yield(Table II) of mature DCs was 4-8×10⁶ at 16d with 60-80% purity. This isat least 20 times the yield of mature DCs in fresh normal blood(Freudenthal, P. S. and R. M. Steinman, (1990) Proc. Natl. Acad. Sci.USA, 87:7698; O'Doherty, et al. (1993) J. Exp. Med., 178:1067).

TABLE II DC Progenitors in Human Blood Type of Enrichment of Time of DCYields/ DC Cytokines Bood Donor DC Progenitors Culture 40 ml BloodEnrichment Added Neonatal, Remove 10-20 d 1-5 × 10⁶ 20-50% GM-CSF cordblood glycophorin⁺ TNFα erythroid cells Adult blood, Remove CD3⁺ 16 d4-8 × 10⁶ 60-80% GM-CSF patients & & HLA-DR⁺ TNFα chemotherapy cells &CSF therapy Adult blood, Bulk PBMC, 5-7 d 3-8 × 10⁶ 40-80% GM-CSF normaladherent & IL-4 loosely adherentK. Proliferating DC aggregates from normal adult blood: When we appliedthe above methods to blood from healthy adults, we did observe somesmall, adherent, veiled aggregates between d8-16. In all 20 experiments,the aggregates then deteriorated and did not enlarge, leaving behindnonviable cells or less often a few macrophages. Because a stromalmonolayer was not evident in the cultures, we next omitted the panningstep with anti-CD3 and HLA-DR in case the panning antibodies removedrequired accessory cells. We simply plated 10⁶ bulk mononuclear cells in1 ml of medium with GM-CSF [800 U/ml] and TNF-α [50 U/ml], and after 1day gently removed the nonadherent lymphocytes. We then observed theadherent cells every 12 h under the inverted microscope. To oursurprise, many small adherent aggregates developed within 2d, and mostwere covered with typical DC veils. However within 2 more days, theaggregated cells became round and gave rise to a monolayer ofmacrophages. These events took place whether GM-CSF, or GM-CSF plusTNF-α were added. However by d12-16 typical expanding DC aggregatesappeared in some of the wells. These aggregates were loosely affixed toan adherent monolayer similar as previously observed in mouse blood(Inaba, et al., (1992) J. Exp. Med., 175:1157) [not shown]. The DCs thatwere released were typical in morphology, phenotype [not shown], and Tcell stimulatory function [FIG. 20C]. The yield was about 4% of theinitial number of mononuclear cells plated, which is far greater thanthe 0.5-1% yield of DCs in fresh blood (Freudenthal, P. S. and R. M.Steinman, (1990) Proc. Natl. Acad. Sci. USA, 87:7698; O'Doherty, et al.(1993) J. Exp. Med., 178:1067).

Not wishing to be bound by theory, we suspect from these findings thatDC precursors were actually quite numerous in blood, but that theprecursor still had the potential to give rise to macrophages. Thelatter is known to be the case for the colony forming units that GM-CSFinduces in mouse (Inaba, et al., (1993) Proc. Natl. Acad. Sci. USA,90:3038). Since IL-4 at 500-1000 U/ml blocks macrophage colony formation(Jansen, et al., (1989) J. Exp. Med., 170:577), we added IL-4 to GM-CSFand repeated the experiments.

The combination of GM-CSF and IL-4 produced two striking findings. Firstthe numerous, initial veiled aggregates [FIG. 21Aa] did not transforminto macrophages but rather increased rapidly in size over the next fewdays [FIG. 21B]. The aggregates became nonadherent, displayed typicalveils all over the periphery, and began to release mature DCs [FIG.21C]. Second, the single adherent cells [presumably monocytes] that werescattered in between the small adherent aggregates, also becamenonadherent and developed processes similar to those of typical DCs [notshown]. Growing DC aggregates only formed in the presence of both GM-CSFand IL-4. The initial nonadherent fraction also developed someaggregates but these were obscured by the excess of lymphocytes.

After having made these observations in 20 experiments, we found itsimpler to use larger 35 mm wells. The protocol was to plate 5-20×10⁶plain bulk mononuclear cells in 3 ml of medium, to discard thenonadherent cells at 2 h with a very gentle rinse, and then to culturethe adherent cells in medium supplemented with GM-CSF [800 U/ml] andIL-4 [500 U/ml]. With the above gentle wash, the nonadherent cells didnot develop DC aggregates, but with more vigorous washing, theaggregates mainly developed in the nonadherent fraction.

The presumptive DC aggregates were verified to be proliferating by twocriteria: staining of ˜10% of the cells with the Ki-67 mAb thatidentifies an antigen in cycling cells (Gerdes, et al., (1984) J.Immunol., 133:1710) [FIG. 22Dd], and sensitivity to 3000 rads. Incontrast the tightly adherent populations, which could develop singlecells with the appearance of DCs [see above], were nonproliferating asevidenced by a lack of staining with anti-K±67 mAb [FIG. 22D] and aresistance to 3000 rads of irradiation.

The combination of GM-CSF and IL-4 reproducibly gives rise to largegrowing DC aggregates over a 5-7d period. At that time, growthessentially ceased. The aggregates then could be disassembled bypipetting into DCs with characteristic morphology at the light [FIG.21C] and EM level [FIG. 24], a typical surface phenotype [FIG. 23], andstrong T cell stimulatory function [FIG. 20D-20F]. Human rIL-1 [50 LAFunits/ml], when added during the last 24 h of culture, amplified thestimulatory function of DCs similar as observed with murine DCs isolatedfrom spleen or epidermis (Heufler, et al., (1988) J. Exp. Med., 167:700;Koide, et al., (1987) J. Exp. Med., 165:515). Interestingly theblood-derived DCs expressed CD1a, CD4, and FceRI as is typical ofepidermal Langerhans cells (Wang, et al., (1992) J. Exp. Med., 175:1353;Romani, N., P., Fritsch, and G. Schuler. (1991). “Identification andphenotype of epidermal Langerhans cells.” In Epdermal Langerhans Cells.G. Schuler, editor. CRC Press, Boca Raton. 49-86; Bieber, et al., (1992)J. Exp. Med., 175:1285). Birbeck granules were not detectable by EMhowever, and only a rare cell in the center of a residual DC aggregatestained with anti-Lag mAb (Kashihara, et al., (1986) J. Invest.Dermatol., 87:602) [FIG. 22C]. Anti-CD68 immunostaining revealed aperinuclear zone of reactivity in some of the DCs [FIG. 22A], a featurethat differs from the strong diffuse granular staining of macrophages[FIG. 22B].

The yield of mature, immunostimulatory DCs (Table II) was 6-15% of themononuclear cells plated. This is many times greater than the number ofDCs that can be identified in unstimulated blood [0.3-1%] (Freudenthal,P. S. and R. M. Steinman, (1990) Proc. Natl. Acad. Sci. USA, 87:7698;O'Doherty, et al. (1993) J. Exp. Med., 178:1067). The above protocol andyield [3-8×10⁶ DCs/40 ml of blood] has proven reproducible in over 25experiments with blood from healthy males and females [25-60 yrs], usingeither fresh venapuncture or buffy coat preparations.

DC Progenitors in Human Blood—Identification:

These findings of necessity appear methodological in nature but in factoutline a pathway whereby the distinct DC lineage can be induced toproliferate and mature from precursors that are relatively plentiful inhuman blood. The methodological caste of our results reflects thedifficulty inherent in identifying precursors and progeny in thisdistinctive immunostimulatory pathway. DCs are not yet known to expressa lineage-specific surface antigen, as is the case with lymphocytes,e.g., CD3, CD19, CD20. A lack of lineage specific markers is alsotypical of the individual human myeloid lineages e.g., monocytes,neutrophils, basophils, eosinophils. However, these other myeloidlineages have distinctive tinctorial properties and distinctive CSF'se.g., M-CSF and G-CSF. DCs in contrast are only known to respond to themultilineage cytokine GM-CSF (Witmer-Pack, et al., (1987) J. Exp. Med.,166:1484; Heufler, et al., (1988) J. Exp. Med., 167:700; Koch, et al.,(1990) J. Exp. Med., 171:159), and their peculiar morphology, phenotypeand function is best outlined with a composite of approaches (Steinman,et al. Annu. Rev. Immunol, 9:271.

Given these inherent difficulties, we searched for criteria that weresimilar to those that had been used to identify immature DC progenitors[e.g., MHC class II negative] in mouse blood (Inaba, et al., (1992) J.Exp. Med., 175:1157) and bone marrow (Inaba, et al., (1992) J. Exp.Med., 176:1693). Mouse DCs proliferate within a characteristic aggregatethat attaches loosely to an underlying stroma and is covered with largesheet-like processes or veils [compare FIGS. 19, 21]. By definingconditions that give rise to such aggregates, at first containing a fewcells but growing to >10 cells in diameter, we could establish thatproliferating DC progenitors are readily detectable in the blood of allhealthy adults, and that one could use these progenitors to generaterelatively large numbers of typical immunostimulatory DCs within 7 days,i.e. 3-8 million of such cells/40 ml of blood.

Like cells derived from mouse blood, the critical finding regardinghuman blood, including blood from normal individuals, is the requirementfor GM-CSF. Cells from normal human blood in the presence of GM-CSFalone were capable of supporting dendritic cell precursors but formedsignificantly fewer large aggregates compared to cells from mouse blood.However, human blood contained significantly larger numbers ofmacrophages. IL-4, a known inhibitor of macrophage colony formation(Jansen, et al., (1989) J. Exp. Med., 170:577), allowed extensive DCgrowth and maturation to ensue [FIG. 21].

DC Progenitors in Human Blood—Cytokine Requirements:

To study the properties of DC progenitors in blood, it is not necessaryto enrich for CD34+ multilineage progenitors which are so rare (<0.1%)in normal blood (Ema, et al., (1990) Blood, 75:1941). The need forexogenous cytokines may vary from one experimental situation to anotherdepending on their endogenous production (e.g. TNF) by cells in theculture. However, it is to date essential to add GM-CSF. Exogenous TNF-αis useful to increase DC numbers and function, as described by Caux etal. (1992) Nature, 360:258), but primarily when one uses cord blood orblood from patients who are receiving, CSF therapy to compensate forchemotherapy. The function of TNF may be to diminish granulocyteproduction Santiago-Schwarz, et al. (1993) Blood, 82:3019; Caux, et al.,(1993) J. Exp. Med., 177:1815), and to enhance responsiveness of anearly pro-genitor to GM-CSF as by inducing a chain of the GM-CSFreceptor (Santiago-Schwartz, et al. (1993), Blood, 82:3019; Caux, etal., (1993) J. Exp. Med., 177:1815). With normal adult blood, IL-4 isthe desired exogenous cytokine that is to be applied in combination withGM-CSF. Without being bound by theory, we suspect that IL-4 acts bysuppressing the monocyte differentiation potential of the DC progenitor(Jansen, et al., (1989) J. Exp. Med., 170:577).

GM-CSF is essential to grow DCs from all sources used. Additionalcytokines required for optimal DC growth from the various sources are,however, strikingly different (TNF α versus IL-4). We suspect that thisis due to the fact that the main DC progenitors involved differ. In cordblood the DC aggregates likely derive from CD34+ cells as preliminaryexperiments (N. Romani, unpublished) have shown that depletion of CD34+cells from the initial inoculum virtually abolishes the formation of DCaggregates. This also readily explains the need to add TNF α which isknown to induce responsiveness to GM-CSF of CD34+ cells(Santiago-Schwartz, et al., Blood, 82:3019; Caux, et al., (1993) J. Exp.Med., 177:1815). Ongoing experiments indicate that IL-4 does not seem toenhance DC development from precursors that arise in cord bloodmononuclear cells supplemented with GM-CSF and TNF-α [D. Brang,unpublished]. We do not yet know, however, whether IL-4 is producedendogenously in such cultures. Endogenous IL-4 might suppress—similar toexogenously added IL-4 in adult blood cultures—the monocytedifferentiation potential of more mature DC progenitors that derive fromCD34+ multilineage progenitors in response to GM-CSF and TNF α. DCdevelopmental pathways in cultures of blood derived from cancer patientsduring hematopoietic recovery are presumably similar to cord blood.Besides CD34+ cells it is, however, likely that more committedprecursors are also involved as the percentage of CD34+ cells in theCD3/HLA-DR depleted mononuclear cell fraction did not strictly correlatewith DC yields. In normal adult blood in response to GM-CSF and TNF αonly after a prolonged culture period (2 weeks) some DC aggregatesemerged likely from early, rare DC progenitors similar to those in cordblood or blood of cancer patients during hematopoietic recovery. Themain DC progenitor(s) in normal adult blood, however, appear(s) to bemore frequent as only 2 days of culture are needed before many DCaggregates appear [FIG. 21]. Prior work in mouse (Inaba, et al., (1993)Proc. Natl. Acd. Sci. USA, 90:3038) and man (Reid., et al., (1992) J.Immunol, 149:2681) has described that the multilineage colonies that areinduced by GM-CSF in semisolid agar cultures contain all 3 types ofmyeloid progeny, i.e. granulocytes, macrophages, and dendritic cells.The principal DC progenitor in normal human peripheral blood seems moredifferentiated since granulocytes do not develop. This committedprogenitor is GM-CSF responsive, and likely bipotential, developing intomacrophages rather than DCs unless its monocyte differentiationpotential is suppressed by IL-4.

REFERENCES

-   1. Steinman, R. M. 1991. The dendritic cell system and its role in    immunogenicity. Ann. Rev. Immunol. 9:271.-   2. Witmer-Pack, M. D., W. Olivier, J. Valinsky, G. Schuler,    and R. M. Steinman. 1987. Granulocyte/macrophage colony-stimulating    factor is essential for the viability and function of cultured    murine epidermal Langerhans cells. J. Exp. Med. 166:1484.-   3. Heufler, C., F. Koch, and G. Schuler. 1987.    Granulocyte-macrophage colony-stimulating factor and interleukin-1    mediate the maturation of murine epidermal Langerhans cells into    potent immunostimulatory dendritic cells. J. Exp. Med. 167:700.-   4. Romani, N., S. Koide, M. Crowley, M. Witmer-Pack, A. M.    Livingstone, C. G. Pathman, K. Inaba, and R. M. Steinman. 1989.    Presentation of exogenous protein antigens by dendritic cells to T    cell clones: intact protein is presented best by immature, epidermal    Langerhans cells. J. Exp. Med. 169:1169.-   5. Inaba, K., N. Romani, and R. M. Steinman. 1989. An    antigen-independent contact mechanism as an early step in    T-cell-proliferative responses to dendritic cells. J. Exp. Med.    170:527.-   6. Pure', E., K. Inaba, M. T. Crowley, L. Tardelli, M. D.    Witmer-Pack, G. Ruberti, G. Fathman, and R. M. Steinman. 1990.    Antigen processing by epidermal Langerhans cells correlates with the    level of biosynthesis of major histocompatibility complex class II    molecules and expression of invariant chain. J. Exp. Med. 172:1459.-   7. Kampgen, E., N. Koch, F. Koch, P. Stoger, C. Heufler, G. Schuler,    and N. Romani. 1991. Class II major histocompatibility complex    molecules of murine dendritic cells: synthesis, sialylation of    invariant chain, and antigen processing capacity are downregulated    upon culture. Proc. Natl. Acad. Sci. USA 88:3014.-   8. Austyn, J. M., J. W. Kupiec-Weglinski, D. F. Hankins, and P. J.    Morris. 1988. Migration patterns of dendritic cells in the mouse.    Homing to T cell-dependent areas of spleen, and binding within    marginal zone. J. Exp. Med. 167:646.-   9. Larsen, C. P., P. J. Morris, and J. M. Austyn. 1990. Migration of    dendritic leukocytes from cardiac allografts into host spleens: a    novel pathway for initiation of rejection. J. Exp. Med. 171:307.-   10. Austyn, J. M., and C. P. Larsen. 1990. Migration patterns of    dendritic leukocytes. Transpl. 49:1.-   11. Veldman, J. E., and E. Kaiserling. 1980. Interdigitating cells.    In The Reticuloendothelial System, Morphology. I. Carr, and W. T.    Daems, editors. Plenum Publishing Corp., New York. 381-416.-   12. Witmer, M. D., and R. M. Steinman. 1984. The anatomy of    peripheral lymphoid organs with emphasis on accessory cells: light    microscopic, immunocytochemical studies of mouse spleen, lymph node    and Peyer's patch. Am. J. Anat. 170:465.-   13. Kraal, G., M. Breel, M. Janse, and G. Bruin. 1986. Langerhans    cells, veiled cells, and interdigitating cells in the mouse    recognized by a monoclonal antibody. J. Exp. Med. 163:981.-   14. Inaba, K., J. P. Metlay, M. T. Crowley, and R. M.    Steinman. 1990. Dendritic cells pulsed with protein antigens in    vitro can prime antigen-specific, MHC-restricted T cells in situ. J.    Exp. Med. 172:631.-   15. Steinman, R. M., D. S. Lustig, and Z. A. Cohn. 1974.    Identification of a novel cell type in peripheral lymphoid organs of    mice. III. Functional properties in vivo. J. Exp. Med. 139:1431.-   16. Pugh, C. W., G. G. MacPherson, and H. W. Steer. 1983.    Characterization of nonlymphoid cells derived from rat peripheral    lymph. J. Exp. Med. 157:1758.-   17. Fossum, S. 1989. The life history of dendritic leukocytes [DL].    In Current Topics in Pathology. O. H. Ivessen, editor.    Springer-Verlag, Berlin. 101-124.-   18. Katz, S. I., K. Tamaki, and D. H. Sachs. 1979. Epidermal    Langerhans cells are derived from cells originating in bone marrow.    Nature 282:324.-   19. Hart, D. N. J., and J. W. Fabre. 1981. Demonstration and    characterization of Ia-positive dendritic cells in the interstitial    connective tissues of rat heart and other tissues, but not brain. J.    Exp. Med. 154:347.-   20. Bowers, W. E., and M. R. Berkowitz. 1986. Differentiation of    dendritic cells in cultures of rat bone marrow cells. J. Exp. Med.    163:872.-   21. Reid, C. D. L., P. R. Fryer, C. Clifford, A. Kirk, J. Tikerpae,    and S. C. Knight. 1990. Identification of hematopoietic progenitors    of macrophages and dendritic Langerhans cells [DL-CFU] in human bone    marrow and peripheral blood. Blood 76:1139.-   22. Kajigaya, S., T. Suda, J. Suda, M. Saito, Y. Miura, M.    Iizuka, S. Kobayashi, N. Minato, and T. Sudo. 1986. A recombinant    murine granulocyte/macrophage (GM) colony-stimulating factor derived    from an inducer T cell line (IH5.5). Functional restriction to GM    progenitor cells. J. Exp. Med. 164:1102.-   23. Agger, R., M. T. Crowley, and M. D. Witmer-Pack. 1990. The    surface of dendritic cells in the mouse as studied with monoclonal    antibodies. Int. Rev. Immunol. 6:89.-   24. Crowley, M., K. Inaba, M. Witmer-Pack, and R. M. Steinman. 1989.    The cell surface of mouse dendritic cells: FACS analyses of    dendritic cells from different tissues including thymus. Cell.    Immunol. 118:108.-   25. Freudenthal, P. S., and R. M. Steinman. 1990. The distinct    surface of human blood dendritic cells, as observed after an    improved isolation method. Proc. Natl. Acad. Sci. USA 87:7698,-   26. Drexhage, H. A., H. Mullink, J. de Groot, J. Clarke, and B. M.    Balfour. 1979. A study of cells present in peripheral lymph of pigs    with special reference to a type of cell resembling the Langerhans    cells. Cell. Tiss. Res. 202:407.-   27. Schuler, G., and R. M. Steinman. 1985. Murine epidermal    Langerhans cells mature into potent immunostimulatory dendritic    cells in vitro. J. Exp. Med. 161:526.-   28. Romani, N., M. Witmer-Pack, M. Crowley, S. Koide, G. Schuler, K.    Inaba, and R. M. Steinman. 1991. Langerhans cells as immature    dendritic cells. CRC Press, Boston. 191-216.-   29. Romani, N., G. Schuler, and P. Fritsch. 1986. Ontogeny of    Ia-positive and Thy-1 positive leukocytes of murine epidermis. J.    Invest. Dermatol. 86:129.-   30. Nussenzweig, M. C., R. M. Steinman, M. D. Witmer, and B.    Gutchinov. 1982. A monoclonal antibody specific for mouse dendritic    cells. Proc. Natl. Acad. Sci. USA 79:161.-   31. Inaba, K., J. P. Metlay, M. T. Crowley, M. Witmer-Pack,    and R. M. Steinman. 1990. Dendritic cells as antigen presenting    cells in vivo. Int. Rev. Immunol. 6:197.-   32. Barclay, A. N., and G. Mayrhofer. 1981. Bone marrow origin of    Ia-positive cells in the medulla of rat thymus. J. Exp. Med.    153:1666.-   33. Rabinowitz, S. S., and S. Gordon. 1991. Macrosialin, a    macrophage-restricted membrane sialoprotein differentially    glycosylated in response to inflammatory stimuli. J. Exp. Med.    174:827.-   34. Agger, R., M. Witmer-Pack, N. Romani, H. Stossel, W. J.    Swiggard, J. P. Metlay, E. Storozynsky, P. Freimuth, and R. M.    Steinman. 1992. Two populations of splenic dendritic cells detected    with M342, a new monoclonal to an intracellular antigen of    interdigitating dendritic cells and some B lymphocytes. J. Leuk.    Biol. 52:34.-   35. Kaplow, L. S. 1981. Cytochemical identification of mononuclear    phagocytes, in “Manual of macrophage methodology” eds H. B.    Herscowitz, H. T. Holden, J. A. Bellanti, and A. Ghaffer. Marcel    Dekker, Inc., New York. 199-207.-   36. Stossel, H., F. Koch, E. Kampgen, P. Stoger, A. Lenz, C.    Heufler, N. Romani, and G. Schuler. 1990. Disappearance of certain    acidic organelles [endosomes and Langerhans cell granules]    accompanies loss of antigen processing capacity upon culture of    epidermal Langerhans cells. J. Exp. Med. 172:1471.-   37. Steinman, R. M., and Z. A. Cohn. 1973. Identification of a novel    cell type in peripheral lymphoid organs of mice. I. Morphology,    quantitation, tissue distribution. J. Exp. Med. 137:1142.-   38. Steinman, R. M., and M. D. Witmer. 1978. Lymphoid dendritic    cells are potent stimulators of the primary mixed leukocyte reaction    in mice. Proc. Natl. Acad. Sci. USA 75:5132.-   39. Scheicher, C., M. Mehlig, R. Zecher, and K. Reske. 1992.    Dendritic cells from mouse bone marrow: in vitro differentiation by    low doses of recombinant granulocyte-macrophage-CSF. J. Immunol.    Methods In Press:-   40. Crowley, M. T., K. Inaba, M. D. Witmer-Pack, S. Gezelter,    and R. M. Steinman. 1990. Use of the fluorescence activated cell    sorter to enrich dendritic cells from mouse spleen. J. Immunol.    Methods 133:55.-   41. Naito, K., K. Inaba, Y. Hirayama, M. Inaba-Miyama, T. Sudo,    and S. Muramatsu. 1989. Macrophage factors which enhance the mixed    leukocyte reaction initiated by dendritic cells. J. Immunol.    142:1834.-   42. Steinman, R. M., G. Kaplan, M. D. Witmer, and Z. A. Cohn. 1979.    Identification of a novel cell-type in peripheral lymphoid organs of    mice. V. Purification of spleen dendritic cells, new surface    markers, and maintenance in vitro. J. Exp. Med. 149:1.

43. Goud, T. J. L. M., C. Schotte, and R. van Furth. 1975.Identification and characterization of the monoblast in mononuclearphagocyte colonies grown in vitro. J. Exp. Med. 142:1180.

-   44. Inaba, K., Steinman, R. M., Witmer-Pack, M., K. Aya, M.    Inaba, T. Sudo, S. Wolpe, and G. Schuler. 1992. Identification of    proliferating dendritic cell precursors in mouse blood. J. Exp. Med.    175:1157.-   45. Britz, J. S., P. W. Askenase, W. Ptak, R. M. Steinman, and R. K.    Gershon. 1982. Specialized antigen-presenting cells: Splenic    dendritic cells, and peritoneal exudate cells induced by    mycobacteria, activate effector T cells that are resistant to    suppression. J. Exp. Med. 155:1344.-   46. Lechler, R. I. and J. R. Batchelor. 1982. Restoration of    immunogenicity to passenger cell-depleted kidney allografts by the    addition of donor strain dendritic cells. J. Exp. Med. 155:31.-   47. Boog, C. J. P., W. M. Kast, H. Th. M. Timmers, J. Boes, L. P. De    Waal, and C. J. M. Melief. 1985. Abolition of specific immune    response defect by immunization with dendritic cells. Nature 318:59.-   48. Faustman, D. L., R. M. Steinman, H. M. Gebel, V.    Hauptfeld, J. M. Davie, and P. E. Lacy. 1984. Prevention of    rejection of murine islet allografts by pretreatment with    anti-dendritic cell antibody. Proc. Natl. Acad. Sci. USA 81:3864.-   49. Iwai, H., S.-I. Kuma, M. M. Inaba, R. A. Good, T. Yamashita, T.    Kumazawa, and S. Ikehara. 1989. Acceptance of murine thyroid    allografts by pretreatment of anti-Ia antibody or anti-dendritic    cell antibody in vitro. Transpl. 47:45.-   50. Havenith, C. E. G., A. J. Breedijk, M. G. H. Betjes, W.    Calame, R. H. J. Beelen, and E. C. M. Hoefsmit. 1992. T cell priming    in situ by intratracheally instilled antigen-pulsed dendritic cells.    Am. J. Resp. Cell & Molec. Biol. Submitted.-   51. Liu, L. M. and G. G. MacPherson. 1993. Antigen acquisition by    dendritic cells: Intestinal dendritic cells acquire antigen    administered orally and can prime naive T cells “in vivo”. J. Exp.    Med. In Press:-   52. Holt, P. G., M. A. Schon-Hegrad, and J. Oliver. 1987. MHC class    II antigen-bearing dendritic cells in pulmonary tissues of the rat.    Regulation of antigen presentation activity by endogenous macrophage    populations. J. Exp. Med. 167:262.-   53. Bujdoso, R., J. Hopkins, B. M. Dutia, P. Young, and I.    McConnell. 1989. Characterization of sheep afferent lymph dendritic    cells and their role in antigen carriage. J. Exp. Med. 170:1285.-   54. Crowley, M., K. Inaba, and R. M. Steinman. 1990. Dendritic cells    are the principal cells in mouse spleen bearing immunogenic    fragments of foreign proteins. J. Exp. Med. 172:383.-   55. Shimonkevitz, R., J. Kappler, P. Marrack, and H. Grey. 1983.    Antigen recognition by H-2-restricted T cells. I. Cell-free antigen    processing. J. Exp. Med. 158:303.-   56. Ziegler, H. K. and E. R. Unanue. 1982. Decrease in macrophage    antigen catabolism caused by ammonia and chloroquine is associated    with inhibition of antigen presentation T cells. Proc. Natl. Acad.    Sci. USA 79:175.-   57. Pancholi, P., A. Mirza, V. Schauf, R. M. Steinman, and N.    Bhardwaj. 1993. Presentation of mycobacterial antigens by human    dendritic cells: lack of transfer from infected macrophages.    Infection and Immunity submitted:-   58. Inaba, K., M. Inaba, N. Romani, H. Aya, M. Deguchi, S.    Ikehara, S. Muramatsu, and R. M. Steinman. 1992. Generation of large    numbers of dendritic cells from mouse bone marrow cultures    supplemented with granulocyte-macrophage colony stimulating    factor. J. Exp. Med. 176:1693.-   59. 1993. Manual of methods for general bacteriology. In P.    Gerhardt, R. G. E. Murray, R. E. Cogtillo, E. W. Nester, W. A.    Wood, N. R. Krieg, and G. B. Philips, editors.-   60. Cohn, Z. A. 1963. The fate of bacteria within phagocytic    cells. I. The degradation of isotopically labeled bacteria by    polymorphonuclear leucocytes and macrophages. J. Exp. Med. 117:27.-   61. Steinman, R. M. and Z. A. Cohn. 1972. The interaction of    particulate horseradish peroxidase (HRP)-anti HRP immune complexes    in mouse peritoneal macrophages in vitro. J. Cell Biol. 55:616.-   62. Ehrenreich, B. A. and Z. A. Cohn. 1967. The uptake and digestion    of iodinated human serum albumin by macrophages in vitro. J. Exp.    Med. 126:941.-   63. Steinman, R. M. and Z. A. Cohn. 1972. The interaction of soluble    horseradish peroxidase in mouse peritoneal macrophages in vitro. J.    Cell Biol. 55:186.-   64. Cohn, Z. A. and B. A. Ehrenreich. 1969. The uptake, storage and    intracellular hydrolysis of carbohydrates by macrophages. J. Exp.    Med. 129:201.-   65. Ehrenreich, B. A. and Z. A. Cohn. 1969. The fate of peptides    pinocytosed by macrophages in vitro. J. Exp. Med. 129:227.-   66. Hunt, D. F., H. Michel, T. A. Dickinson, J. Shabanowitz, A. L.    Cox, K. Sakaguchi, E. Appella, H. M. Grey, and A. Sette. 1992.    Peptides presented to the immune system by the murine class II major    histocompatibility complex molecule I-Ad. Science 256:1817.-   67. Rudensky, A. Y., P. Preston-Hurlburt, S.-C. Hong, A. Barlow,    and C. A. Janeway Jr. 1991. Sequence analysis of peptides bound to    MHC class II molecules. Nature 353:622.-   68. Jensen, P. E. 1988. Protein synthesis in antigen processing. J.    Immunol. 141:2545.-   69. Harding, C. V. and E. R. Unanue. 1990. Quantitation of    antigen-presenting cell MHC class II/peptide complexes necessary for    T-cell stimulation. Nature 346:574.-   70. Demotz, S., H. M. Grey, and A. Sette. 1990. The minimal number    of class II MHC-antigen complexes needed for T cell activation.    Science 249:1028.-   71. Bhardwaj, N., J. W. Young, A. J. Nisanian, J. Baggers, and R. M.    Steinman. 1992. Small amounts of superantigen on dendritic cells are    sufficient to initiate T cell responses. Submitted-   72. Breel, M., R. E. Mebius, and G. Kraal. 1987. Dendritic cells of    the mouse recognized by two monoclonal antibodies. Eur. J. Immunol.    17:1555.-   73. Fossum, S. and B. Rolstad. 1986. The roles of interdigitating    cells and natural killer cells in the rapid rejection of allogeneic    lymphocytes. Eur. J. Immunol. 16:440.-   74. Reis e Sousa, C., P. D. Stahl, and J. M. Austyn. 1993.    Phagocytosis of antigens by langerhans cells in vitro. J. Exp. Med.    In Press.-   75. Harding, C. V., R. W. Roof, an E. R. Unanue. 1990. Turnover of    Ia-peptide complexes is facilitated in viable antigen-presenting    cells: Biosynthetic turnover of Ia vs. peptide exchange. Proc. Natl.    Acad. Sci. USA 86:4230.-   76. Brodsky, F. M. and L. E. Guagliardi. 1991. The cell biology of    antigen processing and presentation. Ann. Rev. Immunol. 9:707.-   77. Nonacs, R., C. Humborg, J. P. Tam, and R. M. Steinman. 1992.    Mechanisms of mouse spleen dendritic cell function in the generation    of influenza-specific, cytolytic T lymphocytes. J. Exp. Med.    176:519.-   78. Freiden, Thomas R., T. Sterling, A. Pablos-Mendez, J.    Kilburn, G. Cauthen and S. W. Dooley, 1993. The emergence of    drug-resistant tuberculosis in New York City. No Eng. J. of Med.    328:521.

While we have hereinbefore described a number of embodiments of thisinvention, it is apparent that the basic constructions can be altered toprovide other embodiments which utilize the methods and compositions ofthis invention. Therefore, it will be appreciated that the scope of thisinvention is defined by the claims appended hereto rather than by thespecific embodiments which have been presented hereinbefore by way ofexample.

1-27. (canceled)
 28. A method of producing a population of dendriticcells comprising the steps of: (a) providing a tissue source comprisingdendritic cell precursors; (b) treating the tissue source to enrich theproportion of dendritic precursor cells; (c) culturing cells obtainedfrom treatment of the tissue source in medium comprising GM-CSF and IL-4for a period of time sufficient to produce dendritic cells.
 29. Themethod according to claim 28, wherein the tissue source is blood. 30.The method according to claim 29, wherein the blood is cord blood. 31.The method according to claim 28, wherein the tissue source is human.32. The method according to claim 28, wherein the tissue sourcecomprises mononuclear cells.
 33. The method according to claim 32,wherein said mononuclear cells include monocytes.
 34. The methodaccording to claim 28, wherein said IL-4 is present in the culturemedium at a concentration of about 500-1000 U/ml.
 35. The methodaccording to claim 28, wherein said GM-CSF is present in the culturemedium at a concentration of about 400-800 U/ml.
 36. The method of claim29, wherein step (b) comprises obtaining a population of leukocytessubstantially free of platelets and red blood cells.
 37. The method ofclaim 28, wherein step (b) comprises removing the majority ofnonadherent, newly-formed granulocytes from the cultures by gentlewashes.
 38. The method of claim 28, wherein step (b) comprises removingundesirable cells by panning using a plastic surface.
 39. The method ofclaim 38, wherein the initial nonadherent fraction of cells is removed.40. The method according to claim 28, wherein said IL-4 is present inthe culture medium at a concentration of about 500-1000 U/ml and whereinsaid GM-CSF is present in the culture medium at a concentration of about400-800 U/ml.
 41. A method of producing a population of 3-8×10⁶dendritic cells comprising the steps of: (a) providing a tissue sourcewhich is blood; (b) treating the blood to enrich the proportion ofdendritic precursor cells; (c) culturing cells obtained from treatmentof the tissue source in medium comprising GM-CSF and IL-4 for a periodof time sufficient to produce dendritic cells; whereby a population of3-8×10⁶ dendritic cells is produced from 40 ml of blood.
 42. A method ofproducing a population of dendritic cells comprising the steps of: (a)providing a tissue source comprising dendritic cell precursors; (b)treating the tissue source to enrich the proportion of dendriticprecursor cells; (c) culturing cells obtained from treatment of thetissue source in medium comprising GM-CSF and IL-13 for a period of timesufficient to produce dendritic cells.